ES6 新增的一些特性

{
  var a = 10;
  let b = 10;
}
console.log(a);  //10
console.log(b);  //error: b is not defined
  
var c = 10;
{
  var c = 20;
}
console.log(c);  //20
  
var d = 10;
{
  let d = 20;
}
console.log(d);  //10

var i=0;
for(var i=0; i<10; i++) {
}
console.log(i);  //10

var j=0;
for(let j=0; j<10; j++) {
}
console.log(j);  //0

console.log(a);  //undefined
console.log(b);  //error: b is not defined

var a = 10;
let b = 10;

console.log(a);  //undefined
console.log(b);  //error: b is not defined
var a = 10;
let b = 10;

/*ES5中字符串处理方法*/
var name = "Jack";
var str1 = ‘my name is ‘ + name;
console.log(str1);  //my name is Jack

/*ES6中字符串处理方法*/
var str2 = `my name is ${name}`;
console.log(str2);  //my name is Jack

/*ES5中函数默认参数处理方法*/
function fn1(height) {
    var height = height || 100;
    console.log(height);
}
fn1();  //100

/*ES6中直接在形参赋值进行设置默认参数*/
function fn2(height = 100) {
    console.log(height);
}
fn2();  //100

/*ES5中定义一个函数变量*/
var fn1 = function(height) {
    console.log(height);
}
fn1(100);  //100

/*ES6中用箭头函数定义函数变量*/
var fn2 = (height) => {
    console.log(height);
}
fn2(100);  //100

/*箭头函数特性：箭头函数的this指针保持和外层指针一致*/
var ele = document.getElementById(‘ele‘);  //获取某个元素，绑定点击事件
ele.onclick = function() {
    setTimeout(function() {
        console.log(this);   //点击后，打印出window对象
    }, 10)
}
ele.onclick = function() {
    setTimeout(() ()=> {
        console.log(this);   //点击后，打印出ele元素对象
    }, 10)
}

/*箭头函数特性：箭头函数的argumets对象和外层一致*/
function fn1(height) {
    setTimeout(function() {
        console.log(arguments);
    }, 10)
}
function fn2(height) {
    setTimeout(() => {
        console.log(arguments);
    }, 10)
}
fn1(100);  //[]
fn2(100);  //[100]

/*ES5初始化变量*/
var a = 10;
var b = 20;

/*ES6解构赋初值*/
var [a, b] = [10, 20];

/*ES5获取对象的key值*/
var obj1 = {
    username1: ‘jack‘,
    password1: 123
}
var username1 = obj1.username1;
var password1 = obj1.password1;
console.log(username1, password1);

/*ES6通过解构拆包获取对象的key值*/
var obj2 = {
    username2: ‘jack‘,
    password2: 123
}
var {username2, password2} = obj2;
console.log(username2, password2);

/*字符串的解构赋值*/
var [a, b, c, d, e] = ‘hello‘;
console.log(a, b, c, d, e);  //h e l l o

/*数组的解构赋值*/
var [a, b, c] = [‘hello‘, ‘world‘];
console.log(a, b, c);  //hello world

//合并数组
var arry = [‘a‘, ‘b‘];
var arry1 = arry.concat([‘c‘]);  //ES5数组拼接
var arry2 = [...arry, ‘c‘];  //ES6...操作符拼接数组
console.log(arry1); //[‘a‘, ‘b‘, ‘c‘]
console.log(arry2);  //[‘a‘, ‘b‘, ‘c‘]

//合并对象
var obj = {a: 1, b: 2};
var obj1 = {...obj, c: 3};
var obj2 = {...obj, a: 3};
console.log(obj1) ; // {a: 1, b: 2, c: 3}
console.log(obj2) ; // {a: 99, b: 2}

/*拆分字符串*/
console.log([...‘hello‘]); // [ "h", "e", "l", "l", "o" ]

/*合并成数组*/
function mergeArr(...Arrys) {
    console.log(arguments);
}
mergeArr(‘a‘, ‘b‘, ‘c‘);  //[‘a‘, ‘b‘, ‘c‘];

/*拆分数组*/
console.log(...[‘a‘, ‘b‘, ‘c‘]);  //a b c

function fn1() {
    var arry = Array.prototype.sort.call(arguments, function(a, b) {
        return a - b;
    })
    console.log(arry);
}
fn1(3,1,5,3,8,6);  //1 3 3 5 6 8

/*...操作符将类数组转换为数组*/
function fn2() {
    var arry = [...arguments].sort(function(a, b) {
        return a - b;
    })
    console.log(arry);
}
fn2(3,1,5,3,8,6);  //1 3 3 5 6 8

console.log(+0 === -0)  //true，错误结果
console.log(NaN === NaN)  //false，错误结果
console.log(Object.is(+0, -0)) // false，正确结果
console.log(Object.is(NaN, NaN)) // true，正确结果

/*普通值的比较*/
console.log(Object.is(‘foo‘, ‘foo‘)) //true
console.log(Object.is({}, {}))  //false

/*使用方法*/
var target = {a: 1, b: 1 };
var source = {c: 1};
console.log(Object.assign(target, source));  //{a: 1, b: 1, c: 1}

/*如果目标对象与源对象有同名属性，或多个源对象有同名属性，则后面的属性会覆盖前面的属性*/
var target = {a: 1, b: 1 };
var source = {a: 20, c: 1};
console.log(Object.assign(target, source));  //{a: 20, b: 1, c: 1}

/*运用：克隆对象*/
function clone(origin) {
  return Object.assign({}, origin);
}
var obj1 = {
    a: 2
}
var obj2 = clone(obj1);
console.log(obj2);  //{a: 2}

/*注意：Object.assign方法实行的是浅拷贝，而不是深拷贝。也就是说，如果源对象某个属性的值是对象，那么目标对象拷贝得到的是这个对象的引用。*/
var obj1 = {a: {b: 1}, c: 1};
var obj2 = Object.assign({}, obj1);
obj2.a.b = 100;
obj2.c = 200;
console.log(obj1);  //{a: {b: 100}, c: 1}

/*运用：合并对象*/
var merge = (...sources) => Object.assign({}, ...sources);
console.log(merge({a: 1}, {b: 2}, {a: 3, c :3}));  //{a: 3, b: 2, c: 3}

var promise = new Promise((reslove, reject) => {
    if(条件成立) ｛
        /*Pending->Resoloved（成功*/
        reslove(); 
    }else {
        /*Pending->Rejected（失败）*/
        reject();
    }
})

/*运用：隔1s打印‘hello’，隔2s打印‘world’*/

/*ES5实现方法*/
setTimeout(function(){
    console.log(‘hello‘)
      setTimeout(function(){
        console.log(‘world‘)
      }, 1000)
}, 1000)  

/*Promise实现方法*/
var wait1000 = (str) => {
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            resolve(str);
        }, 1000)
    })
}

wait1000(‘hello‘).then((data) => {
    console.log(data);
    return wait1000(‘world‘);
}, () => {
    console.log(‘err‘);
}).then((data) => {
    console.log(data);
})