js 遍历对象属性(for in、Object.keys、Object.getOwnProperty) 以及高效地输出 js 数组

js中几种遍历对象的方法，包括for in、Object.keys、Object.getOwnProperty,它们在使用场景方面各有不同。

for in

主要用于遍历对象的可枚举属性，包括自有属性、继承自原型的属性

var obj = {"name":"Poly", "career":"it"}
Object.defineProperty(obj, "age", {value:"forever 18", enumerable:false});
Object.prototype.protoPer1 = function(){console.log("proto");};
Object.prototype.protoPer2 = 2;
console.log("For In : ");
for(var a in obj) console.log(a);

Object.keys

返回一个数组，元素均为对象自有的可枚举属性

var obj = {"name":"Poly", "career":"it"}
Object.defineProperty(obj, "age", {value:"forever 18", enumerable:false});
Object.prototype.protoPer1 = function(){console.log("proto");};
Object.prototype.protoPer2 = 2;
console.log("Object.keys:")
console.log(Object.keys(obj));

 

Object.getOwnProperty

用于返回对象的自有属性，包括可枚举和不可枚举的

var obj = {"name":"Poly", "career":"it"}
Object.defineProperty(obj, "age", {value:"forever 18", enumerable:false});
Object.prototype.protoPer1 = function(){console.log("proto");};
Object.prototype.protoPer2 = 2;
console.log("Object.getOwnPropertyNames: ");
console.log(Object.getOwnPropertyNames(obj));

输出如下：

怎样快速而优雅地遍历 JavaScript 数组

// 最快且优雅的代码
var array = [0,1,2,3,4,5,6,7,8,9];

// while 循环
var i = array.length;
while (i–-) {
    fn(array[i]);
}