Function _keyIterator

public/javascripts/async.js:134–152

(coll)

    };

    function _keyIterator(coll) {
        var i = -1;
        var len;
        var keys;
        if (_isArrayLike(coll)) {
            len = coll.length;
            return function next() {
                i++;
                return i < len ? i : null;
            };
        } else {
            keys = _keys(coll);
            len = keys.length;
            return function next() {
                i++;
                return i < len ? keys[i] : null;
            };
        }
    }

    // Similar to ES6's rest param (http://ariya.ofilabs.com/2013/03/es6-and-rest-parameter.html)
    // This accumulates the arguments passed into an array, after a given index.