array/findIndex.js

define(['../internal/baseCallback'], function(baseCallback) {

  /**
   * This method is like `_.find` except that it returns the index of the first
   * element `predicate` returns truthy for, instead of the element itself.
   *
   * If a property name is provided for `predicate` the created "_.property"
   * style callback returns the property value of the given element.
   *
   * If an object is provided for `predicate` the created "_.matches" style
   * callback returns `true` for elements that have the properties of the given
   * object, else `false`.
   *
   * @static
   * @memberOf _
   * @category Array
   * @param {Array} array The array to search.
   * @param {Function|Object|string} [predicate=_.identity] The function invoked
   *  per iteration. If a property name or object is provided it is used to
   *  create a "_.property" or "_.matches" style callback respectively.
   * @param {*} [thisArg] The `this` binding of `predicate`.
   * @returns {number} Returns the index of the found element, else `-1`.
   * @example
   *
   * var users = [
   *   { 'user': 'barney',  'age': 36, 'active': false },
   *   { 'user': 'fred',    'age': 40, 'active': true },
   *   { 'user': 'pebbles', 'age': 1,  'active': false }
   * ];
   *
   * _.findIndex(users, function(chr) { return chr.age < 40; });
   * // => 0
   *
   * // using the "_.matches" callback shorthand
   * _.findIndex(users, { 'age': 1 });
   * // => 2
   *
   * // using the "_.property" callback shorthand
   * _.findIndex(users, 'active');
   * // => 1
   */
  function findIndex(array, predicate, thisArg) {
    var index = -1,
        length = array ? array.length : 0;

    predicate = baseCallback(predicate, thisArg, 3);
    while (++index < length) {
      if (predicate(array[index], index, array)) {
        return index;
      }
    }
    return -1;
  }

  return findIndex;
});