ES6新特性

1. 变量提升

无论声明在何处，都会被视为声明在函数的最顶部(不在函数内即在全局作用域的最顶部)

var 和let的区别

例：
var

function aa(){
    if(false){
        var test = "Hello World";
    }else{
        console.info(test);//undefined
    }
    console.info(test);//undefined
}
aa();

let

function aa(){
    if(false){
        let test = "Hello World";
    }else{
        console.info(test);//test is not defined
    }
    console.info(test);//test is not defined
}
aa();

var和const区别

例：var

var test = "lidian";
console.log(test);//lidian
test = "lidianmo";
console.log(test);//lidianmo

const

const test = "lidian";
console.log(test);//lidian
test = "lidianmo";
console.log(test);//Uncaught TypeError: Assignment to constant variable.

2. 模板字符串

var name = "lidian";
console.info("name:"+name);//name:lidian
console.info(`name:${name}`);//name:lidian

    // es5
    var msg = "Hi \
    man!"
    // es6
    const template =
    `<div>
        <span>hello world</span>
    </div>`
    console.log(msg);
    console.log(template);

var cludeStr = "ha";
console.log(cludeStr.repeat(3));//hahaha
console.log(cludeStr.includes("e"));//false

3.函数默认参数

function action(num = 200) {
    console.log(num)
}
action() //200
action(0) //200
action(300) //300

4. 箭头函数

• 不需要function关键字来创建函数
• 省略return关键字
• 继承当前上下文的 this 关键字
  例如:

1和2效果是一样的
var people1 = name =>'hello:' + name;
var people2 = function(name){
    return `hello:${name}`;
}

PS:当函数有且仅有一个参数的时候，是可以省略掉括号的。当函数返回有且仅有一个表达式的时候可以省略{}

var people1 = name =>'hello:' + name;
var people2 = function(name){
    return `hello:${name}`;
}
console.log(people1(123));
console.log(people2(456));

var people = (name, age) => {
    const fullName = 'h' + name
    return fullName
}
var people = function(name,age){
    const fullName = 'h' + name
    return fullName
}

5. 拓展的对象功能

1. 对象初始化简写

//ES5    
function people(name, age) {
    return {
        name: name,
        age: age
    };
}
//ES6
function people(name, age) {
    return {
        name,
        age
    };
}

2. 对象中方法赋值，省略方法的冒号与function

    const people = {
        name: 'lux',
        getName: function() {
            console.log(this.name)
        }
    }

    const people = {
        name: 'lux',
        getName () {
            console.log(this.name)
        }
    }

3. Object.assign() 同名的情况，后面会覆盖前面

assign

//ES5    
function people1(name, age) {
    return {
        name: name,
        age: age
    };
}
//ES6
function people2(sex, name) {
    return {
        sex,
        name
    };
}
const p1 = people1("lidian",12);
const p2 = people2("girl","lidianmo");
const obj = Object.assign({}, p1, p2);
console.info(obj);

4. 解构赋值---更方便的数据访问方式