Object.keys 使用实例讲解

// simple array
var arr = ['a', 'b', 'c'];
console.log( .keys(arr)); // console: ['0', '1', '2']

// array like  
var obj = { 0: 'a', 1: 'b', 2: 'c' };
console.log( .keys(obj)); // console: ['0', '1', '2']

// array like   with random key ordering
var anObj = { 100: 'a', 2: 'b', 7: 'c' };
console.log( .keys(anObj)); // console: ['2', '7', '100']

// getFoo is a property which isn't enumerable
var myObj =  .create({}, {
  getFoo: {
    value: function () { return this.foo; }
  } 
});
myObj.foo = 1;
console.log( .keys(myObj)); // console: ['foo']