⛲️ Simple, isolated async waterfall module for JavaScript. Zero dependencies. Runs a list of tasks, passing the results of each into the next one.
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README.md

async-waterfall

Simple, isolated async waterfall module for JavaScript.

Runs an array of functions in series, each passing their results to the next in the array. However, if any of the functions pass an error to the callback, the next function is not executed and the main callback is immediately called with the error.

For browsers and node.js.

Installation

  • Just include async-waterfall before your scripts.
  • npm install async-waterfall if you’re using node.js.
  • component install es128/async-waterfall if you’re using component(1).
  • bower install async-waterfall if you’re using Twitter Bower.

Usage

  • waterfall(tasks, optionalCallback);
  • tasks - An array of functions to run, each function is passed a callback(err, result1, result2, ...) it must call on completion. The first argument is an error (which can be null) and any further arguments will be passed as arguments in order to the next task.
  • optionalCallback - An optional callback to run once all the functions have completed. This will be passed the results of the last task's callback.
Node.js:
var waterfall = require('async-waterfall');
waterfall(tasks, callback);
Browser:
// component(1)
var waterfall = require('async-waterfall');
waterfall(tasks, callback);

// Default:
window.asyncWaterfall(tasks, callback);
Tasks as Array of Functions
waterfall([
  function(callback){
    callback(null, 'one', 'two');
  },
  function(arg1, arg2, callback){
    callback(null, 'three');
  },
  function(arg1, callback){
    // arg1 now equals 'three'
    callback(null, 'done');
  }
], function (err, result) {
  // result now equals 'done'
});
Derive Tasks from an Array.map
/* basic - no arguments */
waterfall(myArray.map(function (arrayItem) {
  return function (nextCallback) {
    // same execution for each item, call the next one when done
    doAsyncThingsWith(arrayItem, nextCallback);
}}));

/* with arguments, initializer function, and final callback */
waterfall([function initializer (firstMapFunction) {
    firstMapFunction(null, initialValue);
  }].concat(myArray.map(function (arrayItem) {
    return function (lastItemResult, nextCallback) {
      // same execution for each item in the array
      var itemResult = doThingsWith(arrayItem, lastItemResult);
      // results carried along from each to the next
      nextCallback(null, itemResult);
}})), function (err, finalResult) {
  // final callback
});

Acknowledgements

Hat tip to Caolan McMahon and Paul Miller, whose prior contributions this is based upon.

License

MIT