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# a-sync-waterfall
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Simple, isolated sync/async waterfall module for JavaScript.
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Runs an array of functions in series, each passing their results to the next in
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the array. However, if any of the functions pass an error to the callback, the
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next function is not executed and the main callback is immediately called with
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the error.
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For browsers and node.js.
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## Installation
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* Just include a-sync-waterfall before your scripts.
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* `npm install a-sync-waterfall` if you’re using node.js.
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## Usage
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* `waterfall(tasks, optionalCallback, forceAsync);`
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* **tasks** - An array of functions to run, each function is passed a
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`callback(err, result1, result2, ...)` it must call on completion. The first
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argument is an error (which can be null) and any further arguments will be
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passed as arguments in order to the next task.
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* **optionalCallback** - An optional callback to run once all the functions have
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completed. This will be passed the results of the last task's callback.
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* **forceAsync** An optional flag that force tasks run asynchronously even if they are sync.
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##### Node.js:
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```javascript
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var waterfall = require('a-sync-waterfall');
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waterfall(tasks, callback);
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```
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##### Browser:
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```javascript
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var waterfall = require('a-sync-waterfall');
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waterfall(tasks, callback);
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// Default:
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window.waterfall(tasks, callback);
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```
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##### Tasks as Array of Functions
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```javascript
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waterfall([
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function(callback){
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callback(null, 'one', 'two');
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},
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function(arg1, arg2, callback){
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callback(null, 'three');
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},
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function(arg1, callback){
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// arg1 now equals 'three'
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callback(null, 'done');
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}
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], function (err, result) {
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// result now equals 'done'
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});
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```
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##### Derive Tasks from an Array.map
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```javascript
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/* basic - no arguments */
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waterfall(myArray.map(function (arrayItem) {
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return function (nextCallback) {
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// same execution for each item, call the next one when done
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doAsyncThingsWith(arrayItem, nextCallback);
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}}));
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/* with arguments, initializer function, and final callback */
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waterfall([function initializer (firstMapFunction) {
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firstMapFunction(null, initialValue);
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}].concat(myArray.map(function (arrayItem) {
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return function (lastItemResult, nextCallback) {
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// same execution for each item in the array
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var itemResult = doThingsWith(arrayItem, lastItemResult);
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// results carried along from each to the next
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nextCallback(null, itemResult);
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}})), function (err, finalResult) {
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// final callback
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});
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```
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## Acknowledgements
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Hat tip to [Caolan McMahon](https://github.com/caolan) and
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[Paul Miller](https://github.com/paulmillr), whose prior contributions this is
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based upon.
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Also [Elan Shanker](https://github.com/es128) from which this rep is forked
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## License
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[MIT](https://raw.github.com/hydiak/a-sync-waterfall/master/LICENSE)
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