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ES6标准新增的一种新函数Arrow Function
let fun = () => { console.log('CSDN');}
//1、没有形参的时候let fun = () => console.log('我是箭头函数'); fun();//2、只有一个形参的时候()可以省略let fun2 = a => console.log(a); fun2('aaa');//3、俩个及俩个以上的形参的时候let fun3 = (x,y) =>console.log(x,y); //函数体只包含一个表达式则省略return 默认返回fun3(24,44);//4、俩个形参以及函数体多条语句表达式let fun4 = (x,y) => { console.log(x,y); return x+y; //必须加return才有返回值}//5、如果要返回对象时需要用小括号包起来,因为大括号被占用解释为代码块了,正确写法let fun5 = ()=>({ foo: x }) //如果x => { foo: x } //则语法出错
function fun() { console.log('Hello CSDN');}
普通函数可以用于构造函数
function A(a){ console.log(arguments);}A("我","爱","C","S", "D", "N"); // ["我","爱","C","S", "D", "N", callee: ƒ, Symbol(Symbol.iterator): ƒ]let B = (b)=>{ console.log(arguments);}B("我","爱","C","S", "D", "N"); // Uncaught ReferenceError: arguments is not definedlet C = (...c) => { console.log(c);}C("我","爱","C","S", "D", "N"); // ["我","爱","C","S", "D", "N"]
在普通函数中,this总是指向调用它的对象,如果用作构造函数,this指向创建的对象实例。
var obj = { a: 10, b: () => { console.log(this.a); // undefined console.log(this); // Window {postMessage: ƒ, blur: ƒ, focus: ƒ, close: ƒ, frames: Window, …} }, c: function() { console.log(this.a); // 10 console.log(this); // {a: 10, b: ƒ, c: ƒ} }}obj.b(); obj.c();
var obj = { a: 10, b: function(){ console.log(this.a); //10 }, c: function() { return ()=>{ console.log(this.a); //10 } }}obj.b(); obj.c()();
let obj2 = { a: 10, b: function(n) { let f = (n) => n + this.a; return f(n); }, c: function(n) { let f = (n) => n + this.a; //此this指向obj2.value let m = { a: 20 }; return f.call(m,n); //f函数并非指向m,只是传入了n参数而已 }};console.log(obj2.b(1)); // 11console.log(obj2.c(1)); // 11
var a = ()=>{ return 1;}function b(){ return 2;}console.log(a.prototype); // undefinedconsole.log(b.prototype); // {constructor: ƒ}
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