index.js

'use strict';

var _keys = require('async.util.keys');
var isArrayLike = require('async.util.isarraylike');

module.exports = 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;
        };
    }
};