es6 等号箭头什么意思

(function(){
    "use strict";
    // use arrow functions here
}());

=>

param => expression

//  一个参数对应一个表达式
param => expression;// 例如 x => x+2;

// 多个参数对应一个表达式
(param [, param]) => expression; //例如 (x,y) => (x + y);

// 一个参数对应多个表示式
param => {statements;} //例如 x = > { x++; return x;};

//  多个参数对应多个表达式
([param] [, param]) => {statements} // 例如 (x,y) => { x++;y++;return x*y;};

//表达式里没有参数
() => expression; //例如var flag = (() => 2)(); flag等于2
() => {statements;} //例如 var flag = (() => {return 1;})(); flag就等于1

//传入一个表达式，返回一个对象
([param]) => ({ key: value });
//例如  var fuc = (x) => ({key:x})
        var object = fuc(1);
        alert(object);//{key:1}

// 当前函数
var func = function (param) {
    return param.split(" ");
}
// 利用箭头函数实现
var func = param => param.split(" ");

func("Felipe Moura"); // returns ["Felipe", "Moura"]

( x => x * 2 )( 3 ); // 6

( (x, y) => {
    x = x * 2;
    return x + y;
})( 3, "A" ); // "6A"

var func = x => {
    return x++;
};

console.log(arguments); // not defined

func instanceof Function; // true
typeof func; // function
func.constructor == Function; // true

//  有效的常规语法
(function (x, y){
    x= x * 2;
    return x + y;
} (3, "B") );
// 无效的箭头函数语法
( (x, y) => {
    x= x * 2;
    return x + y;
} ( 3, "A" ) );
// 但是可以这样写就是有效的了：
( (x,y) => {
    x= x * 2;return x + y;
} )( 3,"A" );//立即执行函数

var instance= new func(); // TypeError: func is not a constructor

func.prototype; // undefined

document.body.addEventListener('click', function(evt){
    console.log(this); // the htmlBodyElement itself
});

function Person () {
    let fullName = null;
    this.getName = function () {
        return fullName;
    };
    this.setName = function (name) {
        fullName = name;
        return this;
    };
}
let jon = new Person();
jon.setName("Jon Doe");
console.log(jon.getName()); // "Jon Doe"
//注：this关键字这里就不解释了，大家自己Google,baidu吧。

jon.setName("Jon Doe")
.getName(); // "Jon Doe"

let obj = {
    foo: "bar",
    getIt: function () {
        return this.foo;
    }
};
console.log( obj.getIt() ); // "bar"

function Student(data){
    this.name = data.name || "Jon Doe";
    this.age = data.age>=0 ? data.age : -1;
    this.getInfo = function () {
        return this.name + ", " + this.age;
    };
    this.sayHi = function () {
        window.setTimeout( function () {
            console.log( this );
        }, 100 );
    }
}

let mary = new Student({
    name: "Mary Lou",
    age: 13
});
console.log( mary.getInfo() ); // "Mary Lou, 13"
mary.sayHi();
// window

function Student(data){
    this.name = data.name || "Jon Doe";
    this.age = data.age>=0 ? data.age : -1;
    this.getInfo = function () {
        return this.name + ", " + this.age;
    };
    this.sayHi = function () {
        window.setTimeout( ()=>{
            // the only difference is here
            console.log( this );
        }, 100 );
    }
}

let mary = new Student({
    name: "Mary Lou",
    age: 13
});
console.log( mary.getInfo() ); // "Mary Lou, 13"
mary.sayHi();
// Object { name: "Mary Lou", age: 13, ... }

var arr = ['a', 'e', 'i', 'o', 'u'];
arr.forEach(vowel => {
    console.log(vowel);
});

//在Array.map里使用箭头函数，这里我就不分析函数执行过程了。。。。

var arr = ['a', 'e', 'i', 'o', 'u'];
arr.map(vowel => {
    return vowel.toUpperCase();
});
// [ "A", "E", "I", "O", "U" ]

var factorial = (n) => {
    if(n==0) {
        return 1;
    }
    return (n * factorial (n-1) );
}
factorial(6); // 720

let arr = ['a', 'e', 'i', 'o', 'u'];
arr.sort( (a, b)=> a < b? 1: -1 );

// EventObject, BodyElement
document.body.addEventListener('click', event=>console.log(event, this));