js 中Object.keys()返回string類型的索引

Object.keys(obj)

參數 obj:要返回其枚舉自身屬性的對象

返回值：一個表示給定對象的所有可枚舉屬性的字符串數組

 如果是key-value的形式，會根據key來排序

eg-

// simple array var arr = ['a', 'b', 'c']; console.log(Object.keys(arr)); // console: ['0', '1', '2'] // array like object var obj = { 0: 'a', 1: 'b', 2: 'c' }; console.log(Object.keys(obj)); // console: ['0', '1', '2'] // array like object with random key ordering var anObj = { 100: 'a', 2: 'b', 7: 'c' }; console.log(Object.keys(anObj)); // console: ['2', '7', '100'] // getFoo is a property which isn't enumerable var myObj = Object.create({}, { getFoo: { value: function () { return this.foo; } } }); myObj.foo = 1; console.log(Object.keys(myObj)); // console: ['foo']