为什么push方法适用于对象？

Question

Why does "push method" works with object? How that mechanism works underhood?

function MyArray() { }
MyArray.prototype = [];

var arr = new MyArray();
arr.push(1, 2, 3);
console.log(arr); // [1, 2, 3]  in Chrome

sorry for my english. Thanks!

Answer 1

MyArray returns an object, even in Chrome, and uses the methods of Array , via assigned prototypal inheritance . The result of an instance of MyArray is still an object, not an array.

 function MyArray() { } MyArray.prototype = []; var arr = new MyArray(); arr.push(1, 2, 3); console.log(arr); // { 0: 1, 1: 2, 2: 3, length: 3 } console.log(typeof arr); // object console.log(Array.isArray(arr)); // false console.log(arr instanceof Array); // true console.log(arr instanceof MyArray); // true