for-each-async

ForEachAsync

Asynchronous Array.forEach. The forEach() method executes a provided function once per array element.

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Installation

$ npm install for-each-async

Syntax

forEachAsync(array, iteratee, done[, thisArg])

Parameters

• array Array - The array to iterate through.

• iteratee Function - The function to execute on each value in the array, taking four arguments:

  • val Any - The current element being processed in the array.

  • n Integer - The index of the current element being processed in the array.

  • arr Array - The array forEachAsync was called upon.

  • next Function - The function to call when you are ready to advance to the next element in the array.

• done Function - The function called when the loop has finished.

• thisArg Object (Optional) - Value to use as this when executing callback.

More information on how forEach works.

Examples

• Asynchronously print the contents of an array.

  The following code logs a line for each element in an array:

  function logArrayElements(val, n, arr, next) {
    console.log('a[' + n + '] = ' + val);
    next();
  }
  
  // Notice that index 2 is skipped since there is no item at
  // that position in the array.
  forEachAsync([2, 5, , 9], logArrayElements, () => {
    console.log('done');
  });
  // logs:
  // a[0] = 2
  // a[1] = 5
  // a[3] = 9
  // done
  

• Asynchronously using thisArg

  The following (contrived) example updates an object's properties from each entry in the array:

  function Counter() {
    this.sum = 0;
    this.count = 0;
  }
  
  Counter.prototype.add = function (array) {
    forEachAsync(array, function (val, n, arr, next) {
      this.sum += entry;
      ++this.count;
      next();
    }, function () {
      // Done
    }, this);
    // ^---- Note
  };
  
  var obj = new Counter();
  obj.add([2, 5, 9]);
  obj.count
  // 3
  obj.sum
  // 16
  

  Since the thisArg parameter (this) is provided to forEachAsync(), it is passed to callback each time it's invoked, for use as its this value.

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Authors

• Nathan Buchar

License

ISC