<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <title>Document</title> </head> <body> <script> // 1.在箭头函数里没有自己的 this 和 arguments let a = { foo: 42, bar: () => { // console.log(this); // console.log(arguments); // 报错 console.log('Inside `bar`:', this.foo); console.log('Inside `bar`:', a.foo); /* Inside `bar`: undefined Inside `bar`: 42 */ }, } a.bar(); // 2.在匿名函数里有 let b = { foo: 42, bar: function() { console.log(this); // {foo: 42, bar: ƒ}bar: ƒ ()foo: 42__proto__: Object console.log(arguments); // Arguments [callee: ƒ, Symbol(Symbol.iterator): ƒ]callee: ƒ ()arguments: nullcaller: nulllength: 0name: "bar"prototype: {constructor: ƒ}__proto__: ƒ ()[[FunctionLocation]]: 箭头函数.html:27[[Scopes]]: Scopes[2]length: 0Symbol(Symbol.iterator): ƒ values()__proto__: Object console.log('Inside `bar`:', this.foo); // Inside `bar`: 42 }, } b.bar(); </script> </body> </html>
箭头函数无法 new
- 箭头函数无法 new
> new (() => {});
TypeError: (intermediate value) is not a constructor
> var x = () => {};
> new x();
TypeError: x is not a constructor
- 匿名函数可以
> new (function() {});
{}
> let f = function() {};
> new f();
f {}