Async filter function for arrays
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README.md

array-async-filter

Filter an array using async filter callback.

Example

example/filter.js:

var asyncFilter = require('..');

asyncFilter(
  ['abc', 'bcd', 'cde', 'def'],
  function (val, i, arr, next) {
    process.nextTick(function () {
      next(null, val.indexOf('cd') !== -1);
    });
  },
  function (err, res) {
    console.log('async callback:', err, res);
  }
);

asyncFilter(
  ['abc', 'bcd', 'cde', 'def'],
  function (val) {
    return new Promise(function (rs) {
      setTimeout(function() {
        rs(val.indexOf('cd') !== -1);
      }, 10);
    });
  },
  function (err, res) {
    console.log('promise callback:', err, res);
  }
);

asyncFilter(
  ['abc', 'bcd', 'cde', 'def'],
  function (val) {
    return val.indexOf('cd') !== -1;
  },
  function (err, res) {
    console.log('sync callback:', err, res);
  }
);

output:

⌘ node example/filter.js
sync callback: null [ 'bcd', 'cde' ]
async callback: null [ 'bcd', 'cde' ]
promise callback: null [ 'bcd', 'cde' ]

asyncFilter(arr, fn, done)

Filter arr using fn, and the results can be accessed by the callback done.

arr

Type: Array

The array to be filtered.

fn

Type: Function

The filter function.

It can be synchronous, with signature fn(val, index, arr). If the returned value is truthy, val will be kept in the final results.

fn can be made asynchronous if it does one of the following.

Accept a callback as the 4th argument

asyncFilter(
  ['abc', 'bcd', 'cde', 'def'],
  function (val, i, arr, next) {
    process.nextTick(function () {
      next(null, val.indexOf('cd') !== -1);
    });
  },
  function (err, res) {
    console.log('async callback:', err, res);
  }
);

Return a promise

asyncFilter(
  ['abc', 'bcd', 'cde', 'def'],
  function (val) {
    return new Promise(function (rs) {
      setTimeout(function() {
        rs(val.indexOf('cd') !== -1);
      }, 10);
    });
  },
  function (err, res) {
    console.log('promise callback:', err, res);
  }
);

done

Type: Function

Signature: done(err, results)

Called when all elements are checked.

If an error is thrown when executing fn, or the next callback is passed a truthy value as the first argument, or the returned promise rejects, done will be called immediately, and filtering finishes.