1  var apply = require('./_apply'),
 2      arrayMap = require('./_arrayMap'),
 3      baseIteratee = require('./_baseIteratee'),
 4      baseRest = require('./_baseRest');
 5  
 6  /** Error message constants. */
 7  var FUNC_ERROR_TEXT = 'Expected a function';
 8  
 9  /**
10   * Creates a function that iterates over `pairs` and invokes the corresponding
11   * function of the first predicate to return truthy. The predicate-function
12   * pairs are invoked with the `this` binding and arguments of the created
13   * function.
14   *
15   * @static
16   * @memberOf _
17   * @since 4.0.0
18   * @category Util
19   * @param {Array} pairs The predicate-function pairs.
20   * @returns {Function} Returns the new composite function.
21   * @example
22   *
23   * var func = _.cond([
24   *   [_.matches({ 'a': 1 }),           _.constant('matches A')],
25   *   [_.conforms({ 'b': _.isNumber }), _.constant('matches B')],
26   *   [_.stubTrue,                      _.constant('no match')]
27   * ]);
28   *
29   * func({ 'a': 1, 'b': 2 });
30   * // => 'matches A'
31   *
32   * func({ 'a': 0, 'b': 1 });
33   * // => 'matches B'
34   *
35   * func({ 'a': '1', 'b': '2' });
36   * // => 'no match'
37   */
38  function cond(pairs) {
39    var length = pairs == null ? 0 : pairs.length,
40        toIteratee = baseIteratee;
41  
42    pairs = !length ? [] : arrayMap(pairs, function(pair) {
43      if (typeof pair[1] != 'function') {
44        throw new TypeError(FUNC_ERROR_TEXT);
45      }
46      return [toIteratee(pair[0]), pair[1]];
47    });
48  
49    return baseRest(function(args) {
50      var index = -1;
51      while (++index < length) {
52        var pair = pairs[index];
53        if (apply(pair[0], this, args)) {
54          return apply(pair[1], this, args);
55        }
56      }
57    });
58  }
59  
60  module.exports = cond;