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  "author": {
    "name": "Caolan McMahon"
  },
  "bugs": {
    "url": "https://github.com/caolan/async/issues"
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  "dependencies": {},
  "description": "Higher-order functions and common patterns for asynchronous code",
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  "readme": "# Async.js\n\nAsync is a utility module which provides straight-forward, powerful functions\nfor working with asynchronous JavaScript. Although originally designed for\nuse with [node.js](http://nodejs.org), it can also be used directly in the\nbrowser. Also supports [component](https://github.com/component/component).\n\nAsync provides around 20 functions that include the usual 'functional'\nsuspects (map, reduce, filter, each…) as well as some common patterns\nfor asynchronous control flow (parallel, series, waterfall…). All these\nfunctions assume you follow the node.js convention of providing a single\ncallback as the last argument of your async function.\n\n\n## Quick Examples\n\n```javascript\nasync.map(['file1','file2','file3'], fs.stat, function(err, results){\n    // results is now an array of stats for each file\n});\n\nasync.filter(['file1','file2','file3'], fs.exists, function(results){\n    // results now equals an array of the existing files\n});\n\nasync.parallel([\n    function(){ ... },\n    function(){ ... }\n], callback);\n\nasync.series([\n    function(){ ... },\n    function(){ ... }\n]);\n```\n\nThere are many more functions available so take a look at the docs below for a\nfull list. This module aims to be comprehensive, so if you feel anything is\nmissing please create a GitHub issue for it.\n\n## Common Pitfalls\n\n### Binding a context to an iterator\n\nThis section is really about bind, not about async. If you are wondering how to\nmake async execute your iterators in a given context, or are confused as to why\na method of another library isn't working as an iterator, study this example:\n\n```js\n// Here is a simple object with an (unnecessarily roundabout) squaring method\nvar AsyncSquaringLibrary = {\n  squareExponent: 2,\n  square: function(number, callback){ \n    var result = Math.pow(number, this.squareExponent);\n    setTimeout(function(){\n      callback(null, result);\n    }, 200);\n  }\n};\n\nasync.map([1, 2, 3], AsyncSquaringLibrary.square, function(err, result){\n  // result is [NaN, NaN, NaN]\n  // This fails because the `this.squareExponent` expression in the square\n  // function is not evaluated in the context of AsyncSquaringLibrary, and is\n  // therefore undefined.\n});\n\nasync.map([1, 2, 3], AsyncSquaringLibrary.square.bind(AsyncSquaringLibrary), function(err, result){\n  // result is [1, 4, 9]\n  // With the help of bind we can attach a context to the iterator before\n  // passing it to async. Now the square function will be executed in its \n  // 'home' AsyncSquaringLibrary context and the value of `this.squareExponent`\n  // will be as expected.\n});\n```\n\n## Download\n\nThe source is available for download from\n[GitHub](http://github.com/caolan/async).\nAlternatively, you can install using Node Package Manager (npm):\n\n    npm install async\n\n__Development:__ [async.js](https://github.com/caolan/async/raw/master/lib/async.js) - 29.6kb Uncompressed\n\n## In the Browser\n\nSo far it's been tested in IE6, IE7, IE8, FF3.6 and Chrome 5. Usage:\n\n```html\n<script type=\"text/javascript\" src=\"async.js\"></script>\n<script type=\"text/javascript\">\n\n    async.map(data, asyncProcess, function(err, results){\n        alert(results);\n    });\n\n</script>\n```\n\n## Documentation\n\n### Collections\n\n* [each](#each)\n* [eachSeries](#eachSeries)\n* [eachLimit](#eachLimit)\n* [map](#map)\n* [mapSeries](#mapSeries)\n* [mapLimit](#mapLimit)\n* [filter](#filter)\n* [filterSeries](#filterSeries)\n* [reject](#reject)\n* [rejectSeries](#rejectSeries)\n* [reduce](#reduce)\n* [reduceRight](#reduceRight)\n* [detect](#detect)\n* [detectSeries](#detectSeries)\n* [sortBy](#sortBy)\n* [some](#some)\n* [every](#every)\n* [concat](#concat)\n* [concatSeries](#concatSeries)\n\n### Control Flow\n\n* [series](#series)\n* [parallel](#parallel)\n* [parallelLimit](#parallellimittasks-limit-callback)\n* [whilst](#whilst)\n* [doWhilst](#doWhilst)\n* [until](#until)\n* [doUntil](#doUntil)\n* [forever](#forever)\n* [waterfall](#waterfall)\n* [compose](#compose)\n* [applyEach](#applyEach)\n* [applyEachSeries](#applyEachSeries)\n* [queue](#queue)\n* [cargo](#cargo)\n* [auto](#auto)\n* [iterator](#iterator)\n* [apply](#apply)\n* [nextTick](#nextTick)\n* [times](#times)\n* [timesSeries](#timesSeries)\n\n### Utils\n\n* [memoize](#memoize)\n* [unmemoize](#unmemoize)\n* [log](#log)\n* [dir](#dir)\n* [noConflict](#noConflict)\n\n\n## Collections\n\n<a name=\"forEach\" />\n<a name=\"each\" />\n### each(arr, iterator, callback)\n\nApplies an iterator function to each item in an array, in parallel.\nThe iterator is called with an item from the list and a callback for when it\nhas finished. If the iterator passes an error to this callback, the main\ncallback for the each function is immediately called with the error.\n\nNote, that since this function applies the iterator to each item in parallel\nthere is no guarantee that the iterator functions will complete in order.\n\n__Arguments__\n\n* arr - An array to iterate over.\n* iterator(item, callback) - A function to apply to each item in the array.\n  The iterator is passed a callback(err) which must be called once it has \n  completed. If no error has occured, the callback should be run without \n  arguments or with an explicit null argument.\n* callback(err) - A callback which is called after all the iterator functions\n  have finished, or an error has occurred.\n\n__Example__\n\n```js\n// assuming openFiles is an array of file names and saveFile is a function\n// to save the modified contents of that file:\n\nasync.each(openFiles, saveFile, function(err){\n    // if any of the saves produced an error, err would equal that error\n});\n```\n\n---------------------------------------\n\n<a name=\"forEachSeries\" />\n<a name=\"eachSeries\" />\n### eachSeries(arr, iterator, callback)\n\nThe same as each only the iterator is applied to each item in the array in\nseries. The next iterator is only called once the current one has completed\nprocessing. This means the iterator functions will complete in order.\n\n\n---------------------------------------\n\n<a name=\"forEachLimit\" />\n<a name=\"eachLimit\" />\n### eachLimit(arr, limit, iterator, callback)\n\nThe same as each only no more than \"limit\" iterators will be simultaneously \nrunning at any time.\n\nNote that the items are not processed in batches, so there is no guarantee that\n the first \"limit\" iterator functions will complete before any others are \nstarted.\n\n__Arguments__\n\n* arr - An array to iterate over.\n* limit - The maximum number of iterators to run at any time.\n* iterator(item, callback) - A function to apply to each item in the array.\n  The iterator is passed a callback(err) which must be called once it has \n  completed. If no error has occured, the callback should be run without \n  arguments or with an explicit null argument.\n* callback(err) - A callback which is called after all the iterator functions\n  have finished, or an error has occurred.\n\n__Example__\n\n```js\n// Assume documents is an array of JSON objects and requestApi is a\n// function that interacts with a rate-limited REST api.\n\nasync.eachLimit(documents, 20, requestApi, function(err){\n    // if any of the saves produced an error, err would equal that error\n});\n```\n\n---------------------------------------\n\n<a name=\"map\" />\n### map(arr, iterator, callback)\n\nProduces a new array of values by mapping each value in the given array through\nthe iterator function. The iterator is called with an item from the array and a\ncallback for when it has finished processing. The callback takes 2 arguments, \nan error and the transformed item from the array. If the iterator passes an\nerror to this callback, the main callback for the map function is immediately\ncalled with the error.\n\nNote, that since this function applies the iterator to each item in parallel\nthere is no guarantee that the iterator functions will complete in order, however\nthe results array will be in the same order as the original array.\n\n__Arguments__\n\n* arr - An array to iterate over.\n* iterator(item, callback) - A function to apply to each item in the array.\n  The iterator is passed a callback(err, transformed) which must be called once \n  it has completed with an error (which can be null) and a transformed item.\n* callback(err, results) - A callback which is called after all the iterator\n  functions have finished, or an error has occurred. Results is an array of the\n  transformed items from the original array.\n\n__Example__\n\n```js\nasync.map(['file1','file2','file3'], fs.stat, function(err, results){\n    // results is now an array of stats for each file\n});\n```\n\n---------------------------------------\n\n<a name=\"mapSeries\" />\n### mapSeries(arr, iterator, callback)\n\nThe same as map only the iterator is applied to each item in the array in\nseries. The next iterator is only called once the current one has completed\nprocessing. The results array will be in the same order as the original.\n\n\n---------------------------------------\n\n<a name=\"mapLimit\" />\n### mapLimit(arr, limit, iterator, callback)\n\nThe same as map only no more than \"limit\" iterators will be simultaneously \nrunning at any time.\n\nNote that the items are not processed in batches, so there is no guarantee that\n the first \"limit\" iterator functions will complete before any others are \nstarted.\n\n__Arguments__\n\n* arr - An array to iterate over.\n* limit - The maximum number of iterators to run at any time.\n* iterator(item, callback) - A function to apply to each item in the array.\n  The iterator is passed a callback(err, transformed) which must be called once \n  it has completed with an error (which can be null) and a transformed item.\n* callback(err, results) - A callback which is called after all the iterator\n  functions have finished, or an error has occurred. Results is an array of the\n  transformed items from the original array.\n\n__Example__\n\n```js\nasync.mapLimit(['file1','file2','file3'], 1, fs.stat, function(err, results){\n    // results is now an array of stats for each file\n});\n```\n\n---------------------------------------\n\n<a name=\"filter\" />\n### filter(arr, iterator, callback)\n\n__Alias:__ select\n\nReturns a new array of all the values which pass an async truth test.\n_The callback for each iterator call only accepts a single argument of true or\nfalse, it does not accept an error argument first!_ This is in-line with the\nway node libraries work with truth tests like fs.exists. This operation is\nperformed in parallel, but the results array will be in the same order as the\noriginal.\n\n__Arguments__\n\n* arr - An array to iterate over.\n* iterator(item, callback) - A truth test to apply to each item in the array.\n  The iterator is passed a callback(truthValue) which must be called with a \n  boolean argument once it has completed.\n* callback(results) - A callback which is called after all the iterator\n  functions have finished.\n\n__Example__\n\n```js\nasync.filter(['file1','file2','file3'], fs.exists, function(results){\n    // results now equals an array of the existing files\n});\n```\n\n---------------------------------------\n\n<a name=\"filterSeries\" />\n### filterSeries(arr, iterator, callback)\n\n__alias:__ selectSeries\n\nThe same as filter only the iterator is applied to each item in the array in\nseries. The next iterator is only called once the current one has completed\nprocessing. The results array will be in the same order as the original.\n\n---------------------------------------\n\n<a name=\"reject\" />\n### reject(arr, iterator, callback)\n\nThe opposite of filter. Removes values that pass an async truth test.\n\n---------------------------------------\n\n<a name=\"rejectSeries\" />\n### rejectSeries(arr, iterator, callback)\n\nThe same as reject, only the iterator is applied to each item in the array\nin series.\n\n\n---------------------------------------\n\n<a name=\"reduce\" />\n### reduce(arr, memo, iterator, callback)\n\n__aliases:__ inject, foldl\n\nReduces a list of values into a single value using an async iterator to return\neach successive step. Memo is the initial state of the reduction. This\nfunction only operates in series. For performance reasons, it may make sense to\nsplit a call to this function into a parallel map, then use the normal\nArray.prototype.reduce on the results. This function is for situations where\neach step in the reduction needs to be async, if you can get the data before\nreducing it then it's probably a good idea to do so.\n\n__Arguments__\n\n* arr - An array to iterate over.\n* memo - The initial state of the reduction.\n* iterator(memo, item, callback) - A function applied to each item in the\n  array to produce the next step in the reduction. The iterator is passed a\n  callback(err, reduction) which accepts an optional error as its first \n  argument, and the state of the reduction as the second. If an error is \n  passed to the callback, the reduction is stopped and the main callback is \n  immediately called with the error.\n* callback(err, result) - A callback which is called after all the iterator\n  functions have finished. Result is the reduced value.\n\n__Example__\n\n```js\nasync.reduce([1,2,3], 0, function(memo, item, callback){\n    // pointless async:\n    process.nextTick(function(){\n        callback(null, memo + item)\n    });\n}, function(err, result){\n    // result is now equal to the last value of memo, which is 6\n});\n```\n\n---------------------------------------\n\n<a name=\"reduceRight\" />\n### reduceRight(arr, memo, iterator, callback)\n\n__Alias:__ foldr\n\nSame as reduce, only operates on the items in the array in reverse order.\n\n\n---------------------------------------\n\n<a name=\"detect\" />\n### detect(arr, iterator, callback)\n\nReturns the first value in a list that passes an async truth test. The\niterator is applied in parallel, meaning the first iterator to return true will\nfire the detect callback with that result. That means the result might not be\nthe first item in the original array (in terms of order) that passes the test.\n\nIf order within the original array is important then look at detectSeries.\n\n__Arguments__\n\n* arr - An array to iterate over.\n* iterator(item, callback) - A truth test to apply to each item in the array.\n  The iterator is passed a callback(truthValue) which must be called with a \n  boolean argument once it has completed.\n* callback(result) - A callback which is called as soon as any iterator returns\n  true, or after all the iterator functions have finished. Result will be\n  the first item in the array that passes the truth test (iterator) or the\n  value undefined if none passed.\n\n__Example__\n\n```js\nasync.detect(['file1','file2','file3'], fs.exists, function(result){\n    // result now equals the first file in the list that exists\n});\n```\n\n---------------------------------------\n\n<a name=\"detectSeries\" />\n### detectSeries(arr, iterator, callback)\n\nThe same as detect, only the iterator is applied to each item in the array\nin series. This means the result is always the first in the original array (in\nterms of array order) that passes the truth test.\n\n\n---------------------------------------\n\n<a name=\"sortBy\" />\n### sortBy(arr, iterator, callback)\n\nSorts a list by the results of running each value through an async iterator.\n\n__Arguments__\n\n* arr - An array to iterate over.\n* iterator(item, callback) - A function to apply to each item in the array.\n  The iterator is passed a callback(err, sortValue) which must be called once it\n  has completed with an error (which can be null) and a value to use as the sort\n  criteria.\n* callback(err, results) - A callback which is called after all the iterator\n  functions have finished, or an error has occurred. Results is the items from\n  the original array sorted by the values returned by the iterator calls.\n\n__Example__\n\n```js\nasync.sortBy(['file1','file2','file3'], function(file, callback){\n    fs.stat(file, function(err, stats){\n        callback(err, stats.mtime);\n    });\n}, function(err, results){\n    // results is now the original array of files sorted by\n    // modified date\n});\n```\n\n---------------------------------------\n\n<a name=\"some\" />\n### some(arr, iterator, callback)\n\n__Alias:__ any\n\nReturns true if at least one element in the array satisfies an async test.\n_The callback for each iterator call only accepts a single argument of true or\nfalse, it does not accept an error argument first!_ This is in-line with the\nway node libraries work with truth tests like fs.exists. Once any iterator\ncall returns true, the main callback is immediately called.\n\n__Arguments__\n\n* arr - An array to iterate over.\n* iterator(item, callback) - A truth test to apply to each item in the array.\n  The iterator is passed a callback(truthValue) which must be called with a \n  boolean argument once it has completed.\n* callback(result) - A callback which is called as soon as any iterator returns\n  true, or after all the iterator functions have finished. Result will be\n  either true or false depending on the values of the async tests.\n\n__Example__\n\n```js\nasync.some(['file1','file2','file3'], fs.exists, function(result){\n    // if result is true then at least one of the files exists\n});\n```\n\n---------------------------------------\n\n<a name=\"every\" />\n### every(arr, iterator, callback)\n\n__Alias:__ all\n\nReturns true if every element in the array satisfies an async test.\n_The callback for each iterator call only accepts a single argument of true or\nfalse, it does not accept an error argument first!_ This is in-line with the\nway node libraries work with truth tests like fs.exists.\n\n__Arguments__\n\n* arr - An array to iterate over.\n* iterator(item, callback) - A truth test to apply to each item in the array.\n  The iterator is passed a callback(truthValue) which must be called with a \n  boolean argument once it has completed.\n* callback(result) - A callback which is called after all the iterator\n  functions have finished. Result will be either true or false depending on\n  the values of the async tests.\n\n__Example__\n\n```js\nasync.every(['file1','file2','file3'], fs.exists, function(result){\n    // if result is true then every file exists\n});\n```\n\n---------------------------------------\n\n<a name=\"concat\" />\n### concat(arr, iterator, callback)\n\nApplies an iterator to each item in a list, concatenating the results. Returns the\nconcatenated list. The iterators are called in parallel, and the results are\nconcatenated as they return. There is no guarantee that the results array will\nbe returned in the original order of the arguments passed to the iterator function.\n\n__Arguments__\n\n* arr - An array to iterate over\n* iterator(item, callback) - A function to apply to each item in the array.\n  The iterator is passed a callback(err, results) which must be called once it \n  has completed with an error (which can be null) and an array of results.\n* callback(err, results) - A callback which is called after all the iterator\n  functions have finished, or an error has occurred. Results is an array containing\n  the concatenated results of the iterator function.\n\n__Example__\n\n```js\nasync.concat(['dir1','dir2','dir3'], fs.readdir, function(err, files){\n    // files is now a list of filenames that exist in the 3 directories\n});\n```\n\n---------------------------------------\n\n<a name=\"concatSeries\" />\n### concatSeries(arr, iterator, callback)\n\nSame as async.concat, but executes in series instead of parallel.\n\n\n## Control Flow\n\n<a name=\"series\" />\n### series(tasks, [callback])\n\nRun an array of functions in series, each one running once the previous\nfunction has completed. If any functions in the series pass an error to its\ncallback, no more functions are run and the callback for the series is\nimmediately called with the value of the error. Once the tasks have completed,\nthe results are passed to the final callback as an array.\n\nIt is also possible to use an object instead of an array. Each property will be\nrun as a function and the results will be passed to the final callback as an object\ninstead of an array. This can be a more readable way of handling results from\nasync.series.\n\n\n__Arguments__\n\n* tasks - An array or object containing functions to run, each function is passed\n  a callback(err, result) it must call on completion with an error (which can\n  be null) and an optional result value.\n* callback(err, results) - An optional callback to run once all the functions\n  have completed. This function gets a results array (or object) containing all \n  the result arguments passed to the task callbacks.\n\n__Example__\n\n```js\nasync.series([\n    function(callback){\n        // do some stuff ...\n        callback(null, 'one');\n    },\n    function(callback){\n        // do some more stuff ...\n        callback(null, 'two');\n    }\n],\n// optional callback\nfunction(err, results){\n    // results is now equal to ['one', 'two']\n});\n\n\n// an example using an object instead of an array\nasync.series({\n    one: function(callback){\n        setTimeout(function(){\n            callback(null, 1);\n        }, 200);\n    },\n    two: function(callback){\n        setTimeout(function(){\n            callback(null, 2);\n        }, 100);\n    }\n},\nfunction(err, results) {\n    // results is now equal to: {one: 1, two: 2}\n});\n```\n\n---------------------------------------\n\n<a name=\"parallel\" />\n### parallel(tasks, [callback])\n\nRun an array of functions in parallel, without waiting until the previous\nfunction has completed. If any of the functions pass an error to its\ncallback, the main callback is immediately called with the value of the error.\nOnce the tasks have completed, the results are passed to the final callback as an\narray.\n\nIt is also possible to use an object instead of an array. Each property will be\nrun as a function and the results will be passed to the final callback as an object\ninstead of an array. This can be a more readable way of handling results from\nasync.parallel.\n\n\n__Arguments__\n\n* tasks - An array or object containing functions to run, each function is passed \n  a callback(err, result) it must call on completion with an error (which can\n  be null) and an optional result value.\n* callback(err, results) - An optional callback to run once all the functions\n  have completed. This function gets a results array (or object) containing all \n  the result arguments passed to the task callbacks.\n\n__Example__\n\n```js\nasync.parallel([\n    function(callback){\n        setTimeout(function(){\n            callback(null, 'one');\n        }, 200);\n    },\n    function(callback){\n        setTimeout(function(){\n            callback(null, 'two');\n        }, 100);\n    }\n],\n// optional callback\nfunction(err, results){\n    // the results array will equal ['one','two'] even though\n    // the second function had a shorter timeout.\n});\n\n\n// an example using an object instead of an array\nasync.parallel({\n    one: function(callback){\n        setTimeout(function(){\n            callback(null, 1);\n        }, 200);\n    },\n    two: function(callback){\n        setTimeout(function(){\n            callback(null, 2);\n        }, 100);\n    }\n},\nfunction(err, results) {\n    // results is now equals to: {one: 1, two: 2}\n});\n```\n\n---------------------------------------\n\n<a name=\"parallel\" />\n### parallelLimit(tasks, limit, [callback])\n\nThe same as parallel only the tasks are executed in parallel with a maximum of \"limit\" \ntasks executing at any time.\n\nNote that the tasks are not executed in batches, so there is no guarantee that \nthe first \"limit\" tasks will complete before any others are started.\n\n__Arguments__\n\n* tasks - An array or object containing functions to run, each function is passed \n  a callback(err, result) it must call on completion with an error (which can\n  be null) and an optional result value.\n* limit - The maximum number of tasks to run at any time.\n* callback(err, results) - An optional callback to run once all the functions\n  have completed. This function gets a results array (or object) containing all \n  the result arguments passed to the task callbacks.\n\n---------------------------------------\n\n<a name=\"whilst\" />\n### whilst(test, fn, callback)\n\nRepeatedly call fn, while test returns true. Calls the callback when stopped,\nor an error occurs.\n\n__Arguments__\n\n* test() - synchronous truth test to perform before each execution of fn.\n* fn(callback) - A function to call each time the test passes. The function is\n  passed a callback(err) which must be called once it has completed with an \n  optional error argument.\n* callback(err) - A callback which is called after the test fails and repeated\n  execution of fn has stopped.\n\n__Example__\n\n```js\nvar count = 0;\n\nasync.whilst(\n    function () { return count < 5; },\n    function (callback) {\n        count++;\n        setTimeout(callback, 1000);\n    },\n    function (err) {\n        // 5 seconds have passed\n    }\n);\n```\n\n---------------------------------------\n\n<a name=\"doWhilst\" />\n### doWhilst(fn, test, callback)\n\nThe post check version of whilst. To reflect the difference in the order of operations `test` and `fn` arguments are switched. `doWhilst` is to `whilst` as `do while` is to `while` in plain JavaScript.\n\n---------------------------------------\n\n<a name=\"until\" />\n### until(test, fn, callback)\n\nRepeatedly call fn, until test returns true. Calls the callback when stopped,\nor an error occurs.\n\nThe inverse of async.whilst.\n\n---------------------------------------\n\n<a name=\"doUntil\" />\n### doUntil(fn, test, callback)\n\nLike doWhilst except the test is inverted. Note the argument ordering differs from `until`.\n\n---------------------------------------\n\n<a name=\"forever\" />\n### forever(fn, callback)\n\nCalls the asynchronous function 'fn' repeatedly, in series, indefinitely.\nIf an error is passed to fn's callback then 'callback' is called with the\nerror, otherwise it will never be called.\n\n---------------------------------------\n\n<a name=\"waterfall\" />\n### waterfall(tasks, [callback])\n\nRuns an array of functions in series, each passing their results to the next in\nthe array. However, if any of the functions pass an error to the callback, the\nnext function is not executed and the main callback is immediately called with\nthe error.\n\n__Arguments__\n\n* tasks - An array of functions to run, each function is passed a \n  callback(err, result1, result2, ...) it must call on completion. The first\n  argument is an error (which can be null) and any further arguments will be \n  passed as arguments in order to the next task.\n* callback(err, [results]) - An optional callback to run once all the functions\n  have completed. This will be passed the results of the last task's callback.\n\n\n\n__Example__\n\n```js\nasync.waterfall([\n    function(callback){\n        callback(null, 'one', 'two');\n    },\n    function(arg1, arg2, callback){\n        callback(null, 'three');\n    },\n    function(arg1, callback){\n        // arg1 now equals 'three'\n        callback(null, 'done');\n    }\n], function (err, result) {\n   // result now equals 'done'    \n});\n```\n\n---------------------------------------\n<a name=\"compose\" />\n### compose(fn1, fn2...)\n\nCreates a function which is a composition of the passed asynchronous\nfunctions. Each function consumes the return value of the function that\nfollows. Composing functions f(), g() and h() would produce the result of\nf(g(h())), only this version uses callbacks to obtain the return values.\n\nEach function is executed with the `this` binding of the composed function.\n\n__Arguments__\n\n* functions... - the asynchronous functions to compose\n\n\n__Example__\n\n```js\nfunction add1(n, callback) {\n    setTimeout(function () {\n        callback(null, n + 1);\n    }, 10);\n}\n\nfunction mul3(n, callback) {\n    setTimeout(function () {\n        callback(null, n * 3);\n    }, 10);\n}\n\nvar add1mul3 = async.compose(mul3, add1);\n\nadd1mul3(4, function (err, result) {\n   // result now equals 15\n});\n```\n\n---------------------------------------\n<a name=\"applyEach\" />\n### applyEach(fns, args..., callback)\n\nApplies the provided arguments to each function in the array, calling the\ncallback after all functions have completed. If you only provide the first\nargument then it will return a function which lets you pass in the\narguments as if it were a single function call.\n\n__Arguments__\n\n* fns - the asynchronous functions to all call with the same arguments\n* args... - any number of separate arguments to pass to the function\n* callback - the final argument should be the callback, called when all\n  functions have completed processing\n\n\n__Example__\n\n```js\nasync.applyEach([enableSearch, updateSchema], 'bucket', callback);\n\n// partial application example:\nasync.each(\n    buckets,\n    async.applyEach([enableSearch, updateSchema]),\n    callback\n);\n```\n\n---------------------------------------\n\n<a name=\"applyEachSeries\" />\n### applyEachSeries(arr, iterator, callback)\n\nThe same as applyEach only the functions are applied in series.\n\n---------------------------------------\n\n<a name=\"queue\" />\n### queue(worker, concurrency)\n\nCreates a queue object with the specified concurrency. Tasks added to the\nqueue will be processed in parallel (up to the concurrency limit). If all\nworkers are in progress, the task is queued until one is available. Once\na worker has completed a task, the task's callback is called.\n\n__Arguments__\n\n* worker(task, callback) - An asynchronous function for processing a queued\n  task, which must call its callback(err) argument when finished, with an \n  optional error as an argument.\n* concurrency - An integer for determining how many worker functions should be\n  run in parallel.\n\n__Queue objects__\n\nThe queue object returned by this function has the following properties and\nmethods:\n\n* length() - a function returning the number of items waiting to be processed.\n* concurrency - an integer for determining how many worker functions should be\n  run in parallel. This property can be changed after a queue is created to\n  alter the concurrency on-the-fly.\n* push(task, [callback]) - add a new task to the queue, the callback is called\n  once the worker has finished processing the task.\n  instead of a single task, an array of tasks can be submitted. the respective callback is used for every task in the list.\n* unshift(task, [callback]) - add a new task to the front of the queue.\n* saturated - a callback that is called when the queue length hits the concurrency and further tasks will be queued\n* empty - a callback that is called when the last item from the queue is given to a worker\n* drain - a callback that is called when the last item from the queue has returned from the worker\n\n__Example__\n\n```js\n// create a queue object with concurrency 2\n\nvar q = async.queue(function (task, callback) {\n    console.log('hello ' + task.name);\n    callback();\n}, 2);\n\n\n// assign a callback\nq.drain = function() {\n    console.log('all items have been processed');\n}\n\n// add some items to the queue\n\nq.push({name: 'foo'}, function (err) {\n    console.log('finished processing foo');\n});\nq.push({name: 'bar'}, function (err) {\n    console.log('finished processing bar');\n});\n\n// add some items to the queue (batch-wise)\n\nq.push([{name: 'baz'},{name: 'bay'},{name: 'bax'}], function (err) {\n    console.log('finished processing bar');\n});\n\n// add some items to the front of the queue\n\nq.unshift({name: 'bar'}, function (err) {\n    console.log('finished processing bar');\n});\n```\n\n---------------------------------------\n\n<a name=\"cargo\" />\n### cargo(worker, [payload])\n\nCreates a cargo object with the specified payload. Tasks added to the\ncargo will be processed altogether (up to the payload limit). If the\nworker is in progress, the task is queued until it is available. Once\nthe worker has completed some tasks, each callback of those tasks is called.\n\n__Arguments__\n\n* worker(tasks, callback) - An asynchronous function for processing an array of\n  queued tasks, which must call its callback(err) argument when finished, with \n  an optional error as an argument.\n* payload - An optional integer for determining how many tasks should be\n  processed per round; if omitted, the default is unlimited.\n\n__Cargo objects__\n\nThe cargo object returned by this function has the following properties and\nmethods:\n\n* length() - a function returning the number of items waiting to be processed.\n* payload - an integer for determining how many tasks should be\n  process per round. This property can be changed after a cargo is created to\n  alter the payload on-the-fly.\n* push(task, [callback]) - add a new task to the queue, the callback is called\n  once the worker has finished processing the task.\n  instead of a single task, an array of tasks can be submitted. the respective callback is used for every task in the list.\n* saturated - a callback that is called when the queue length hits the concurrency and further tasks will be queued\n* empty - a callback that is called when the last item from the queue is given to a worker\n* drain - a callback that is called when the last item from the queue has returned from the worker\n\n__Example__\n\n```js\n// create a cargo object with payload 2\n\nvar cargo = async.cargo(function (tasks, callback) {\n    for(var i=0; i<tasks.length; i++){\n      console.log('hello ' + tasks[i].name);\n    }\n    callback();\n}, 2);\n\n\n// add some items\n\ncargo.push({name: 'foo'}, function (err) {\n    console.log('finished processing foo');\n});\ncargo.push({name: 'bar'}, function (err) {\n    console.log('finished processing bar');\n});\ncargo.push({name: 'baz'}, function (err) {\n    console.log('finished processing baz');\n});\n```\n\n---------------------------------------\n\n<a name=\"auto\" />\n### auto(tasks, [callback])\n\nDetermines the best order for running functions based on their requirements.\nEach function can optionally depend on other functions being completed first,\nand each function is run as soon as its requirements are satisfied. If any of\nthe functions pass an error to their callback, that function will not complete\n(so any other functions depending on it will not run) and the main callback\nwill be called immediately with the error. Functions also receive an object\ncontaining the results of functions which have completed so far.\n\nNote, all functions are called with a results object as a second argument, \nso it is unsafe to pass functions in the tasks object which cannot handle the\nextra argument. For example, this snippet of code:\n\n```js\nasync.auto({\n  readData: async.apply(fs.readFile, 'data.txt', 'utf-8')\n}, callback);\n```\n\nwill have the effect of calling readFile with the results object as the last\nargument, which will fail:\n\n```js\nfs.readFile('data.txt', 'utf-8', cb, {});\n```\n\nInstead, wrap the call to readFile in a function which does not forward the \nresults object:\n\n```js\nasync.auto({\n  readData: function(cb, results){\n    fs.readFile('data.txt', 'utf-8', cb);\n  }\n}, callback);\n```\n\n__Arguments__\n\n* tasks - An object literal containing named functions or an array of\n  requirements, with the function itself the last item in the array. The key\n  used for each function or array is used when specifying requirements. The \n  function receives two arguments: (1) a callback(err, result) which must be \n  called when finished, passing an error (which can be null) and the result of \n  the function's execution, and (2) a results object, containing the results of\n  the previously executed functions.\n* callback(err, results) - An optional callback which is called when all the\n  tasks have been completed. The callback will receive an error as an argument\n  if any tasks pass an error to their callback. Results will always be passed\n\tbut if an error occurred, no other tasks will be performed, and the results\n\tobject will only contain partial results.\n  \n\n__Example__\n\n```js\nasync.auto({\n    get_data: function(callback){\n        // async code to get some data\n    },\n    make_folder: function(callback){\n        // async code to create a directory to store a file in\n        // this is run at the same time as getting the data\n    },\n    write_file: ['get_data', 'make_folder', function(callback){\n        // once there is some data and the directory exists,\n        // write the data to a file in the directory\n        callback(null, filename);\n    }],\n    email_link: ['write_file', function(callback, results){\n        // once the file is written let's email a link to it...\n        // results.write_file contains the filename returned by write_file.\n    }]\n});\n```\n\nThis is a fairly trivial example, but to do this using the basic parallel and\nseries functions would look like this:\n\n```js\nasync.parallel([\n    function(callback){\n        // async code to get some data\n    },\n    function(callback){\n        // async code to create a directory to store a file in\n        // this is run at the same time as getting the data\n    }\n],\nfunction(err, results){\n    async.series([\n        function(callback){\n            // once there is some data and the directory exists,\n            // write the data to a file in the directory\n        },\n        function(callback){\n            // once the file is written let's email a link to it...\n        }\n    ]);\n});\n```\n\nFor a complicated series of async tasks using the auto function makes adding\nnew tasks much easier and makes the code more readable.\n\n\n---------------------------------------\n\n<a name=\"iterator\" />\n### iterator(tasks)\n\nCreates an iterator function which calls the next function in the array,\nreturning a continuation to call the next one after that. It's also possible to\n'peek' the next iterator by doing iterator.next().\n\nThis function is used internally by the async module but can be useful when\nyou want to manually control the flow of functions in series.\n\n__Arguments__\n\n* tasks - An array of functions to run.\n\n__Example__\n\n```js\nvar iterator = async.iterator([\n    function(){ sys.p('one'); },\n    function(){ sys.p('two'); },\n    function(){ sys.p('three'); }\n]);\n\nnode> var iterator2 = iterator();\n'one'\nnode> var iterator3 = iterator2();\n'two'\nnode> iterator3();\n'three'\nnode> var nextfn = iterator2.next();\nnode> nextfn();\n'three'\n```\n\n---------------------------------------\n\n<a name=\"apply\" />\n### apply(function, arguments..)\n\nCreates a continuation function with some arguments already applied, a useful\nshorthand when combined with other control flow functions. Any arguments\npassed to the returned function are added to the arguments originally passed\nto apply.\n\n__Arguments__\n\n* function - The function you want to eventually apply all arguments to.\n* arguments... - Any number of arguments to automatically apply when the\n  continuation is called.\n\n__Example__\n\n```js\n// using apply\n\nasync.parallel([\n    async.apply(fs.writeFile, 'testfile1', 'test1'),\n    async.apply(fs.writeFile, 'testfile2', 'test2'),\n]);\n\n\n// the same process without using apply\n\nasync.parallel([\n    function(callback){\n        fs.writeFile('testfile1', 'test1', callback);\n    },\n    function(callback){\n        fs.writeFile('testfile2', 'test2', callback);\n    }\n]);\n```\n\nIt's possible to pass any number of additional arguments when calling the\ncontinuation:\n\n```js\nnode> var fn = async.apply(sys.puts, 'one');\nnode> fn('two', 'three');\none\ntwo\nthree\n```\n\n---------------------------------------\n\n<a name=\"nextTick\" />\n### nextTick(callback)\n\nCalls the callback on a later loop around the event loop. In node.js this just\ncalls process.nextTick, in the browser it falls back to setImmediate(callback)\nif available, otherwise setTimeout(callback, 0), which means other higher priority\nevents may precede the execution of the callback.\n\nThis is used internally for browser-compatibility purposes.\n\n__Arguments__\n\n* callback - The function to call on a later loop around the event loop.\n\n__Example__\n\n```js\nvar call_order = [];\nasync.nextTick(function(){\n    call_order.push('two');\n    // call_order now equals ['one','two']\n});\ncall_order.push('one')\n```\n\n<a name=\"times\" />\n### times(n, callback)\n\nCalls the callback n times and accumulates results in the same manner\nyou would use with async.map.\n\n__Arguments__\n\n* n - The number of times to run the function.\n* callback - The function to call n times.\n\n__Example__\n\n```js\n// Pretend this is some complicated async factory\nvar createUser = function(id, callback) {\n  callback(null, {\n    id: 'user' + id\n  })\n}\n// generate 5 users\nasync.times(5, function(n, next){\n    createUser(n, function(err, user) {\n      next(err, user)\n    })\n}, function(err, users) {\n  // we should now have 5 users\n});\n```\n\n<a name=\"timesSeries\" />\n### timesSeries(n, callback)\n\nThe same as times only the iterator is applied to each item in the array in\nseries. The next iterator is only called once the current one has completed\nprocessing. The results array will be in the same order as the original.\n\n\n## Utils\n\n<a name=\"memoize\" />\n### memoize(fn, [hasher])\n\nCaches the results of an async function. When creating a hash to store function\nresults against, the callback is omitted from the hash and an optional hash\nfunction can be used.\n\nThe cache of results is exposed as the `memo` property of the function returned\nby `memoize`.\n\n__Arguments__\n\n* fn - the function you to proxy and cache results from.\n* hasher - an optional function for generating a custom hash for storing\n  results, it has all the arguments applied to it apart from the callback, and\n  must be synchronous.\n\n__Example__\n\n```js\nvar slow_fn = function (name, callback) {\n    // do something\n    callback(null, result);\n};\nvar fn = async.memoize(slow_fn);\n\n// fn can now be used as if it were slow_fn\nfn('some name', function () {\n    // callback\n});\n```\n\n<a name=\"unmemoize\" />\n### unmemoize(fn)\n\nUndoes a memoized function, reverting it to the original, unmemoized\nform. Comes handy in tests.\n\n__Arguments__\n\n* fn - the memoized function\n\n<a name=\"log\" />\n### log(function, arguments)\n\nLogs the result of an async function to the console. Only works in node.js or\nin browsers that support console.log and console.error (such as FF and Chrome).\nIf multiple arguments are returned from the async function, console.log is\ncalled on each argument in order.\n\n__Arguments__\n\n* function - The function you want to eventually apply all arguments to.\n* arguments... - Any number of arguments to apply to the function.\n\n__Example__\n\n```js\nvar hello = function(name, callback){\n    setTimeout(function(){\n        callback(null, 'hello ' + name);\n    }, 1000);\n};\n```\n```js\nnode> async.log(hello, 'world');\n'hello world'\n```\n\n---------------------------------------\n\n<a name=\"dir\" />\n### dir(function, arguments)\n\nLogs the result of an async function to the console using console.dir to\ndisplay the properties of the resulting object. Only works in node.js or\nin browsers that support console.dir and console.error (such as FF and Chrome).\nIf multiple arguments are returned from the async function, console.dir is\ncalled on each argument in order.\n\n__Arguments__\n\n* function - The function you want to eventually apply all arguments to.\n* arguments... - Any number of arguments to apply to the function.\n\n__Example__\n\n```js\nvar hello = function(name, callback){\n    setTimeout(function(){\n        callback(null, {hello: name});\n    }, 1000);\n};\n```\n```js\nnode> async.dir(hello, 'world');\n{hello: 'world'}\n```\n\n---------------------------------------\n\n<a name=\"noConflict\" />\n### noConflict()\n\nChanges the value of async back to its original value, returning a reference to the\nasync object.\n",
  "readmeFilename": "README.md",
  "repository": {
    "type": "git",
    "url": "git+https://github.com/caolan/async.git"
  },
  "scripts": {
    "test": "nodeunit test/test-async.js"
  },
  "version": "0.2.10"
}
