Object.keys方法实现

object.keys.js

Object.keys = (function () {
            var hasOwnProperty = Object.prototype.hasOwnProperty,
                    hasDontEnumBug = !({toString:null}).propertyIsEnumerable('toString'),
                    dontEnums = [
                        'toString',
                        'toLocaleString',
                        'valueOf',
                        'hasOwnProperty',
                        'isPrototypeOf',
                        'propertyIsEnumerable',
                        'constructor'
                    ],
                    dontEnumsLength = dontEnums.length;

            return function (obj) {
                if (typeof obj !== 'object' && typeof obj !== 'function' || obj === null) throw new TypeError('Object.keys called on non-object')

                var result = [];

                for (var prop in obj) {
                    if (hasOwnProperty.call(obj, prop)) {result.push(prop);}
                }

                if (hasDontEnumBug) {
                    for (var i = 0; i < dontEnumsLength; i++) {
                        if (hasOwnProperty.call(obj, dontEnums[i])) { result.push(dontEnums[i])}
                    }
                }
                return result
            }
        })();