SOURCE

Array.prototype.method=function(){
　　console.log(this.length);
}
var myArray=[1,2,4,5,6,7]
myArray.name="数组"
// for (let index in myArray) {
//     // if (myArray.hasOwnProperty(index)) {
//         console.log(myArray[index]);
//     // }
// }
console.log(Object.keys(myArray))
console.log(myArray['name'])

// for (let key of myArray) {
//     console.log(key)
// }

const obj = {
    a: 'a',
    b: function() {alert(this.a)}
}
let fn = obj.b
fn() // fn 指向 windows