toArray.js

/**
 * Copyright 2014, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 *
 * @providesModule toArray
 * @typechecks
 */

var invariant = require('invariant');

/**
 * Convert array-like objects to arrays.
 *
 * This API assumes the caller knows the contents of the data type. For less
 * well defined inputs use createArrayFrom.
 *
 * @param {object|function|filelist} obj
 * @return {array}
 */
function toArray(obj) {
  var length = obj.length;

  // Some browse builtin objects can report typeof 'function' (e.g. NodeList in
  // old versions of Safari).
  invariant(
    !Array.isArray(obj) &&
    (typeof obj === 'object' || typeof obj === 'function'),
    'toArray: Array-like object expected'
  );

  invariant(
    typeof length === 'number',
    'toArray: Object needs a length property'
  );

  invariant(
    length === 0 ||
    (length - 1) in obj,
    'toArray: Object should have keys for indices'
  );

  // Old IE doesn't give collections access to hasOwnProperty. Assume inputs
  // without method will throw during the slice call and skip straight to the
  // fallback.
  if (obj.hasOwnProperty) {
    try {
      return Array.prototype.slice.call(obj);
    } catch (e) {
      // IE < 9 does not support Array#slice on collections objects
    }
  }

  // Fall back to copying key by key. This assumes all keys have a value,
  // so will not preserve sparsely populated inputs.
  var ret = Array(length);
  for (var ii = 0; ii < length; ii++) {
    ret[ii] = obj[ii];
  }
  return ret;
}

module.exports = toArray;