es other common functions

es6 addition to modular, class, promise, there are some other common functions.

1、let/const

let is to define a variable, but this variable can be reassigned, const is to define a constant, this constant can not be reassigned

I = 10 the let; I = 100; // correct 
const = 20 is J; J = 200 is; // given

 

2, multi-line strings / template variables

// JS
var name = 'zhangsan', age = 20, html = '';
html = '<div>'
html += ' <p>' + name + '</p>';
html += ' <p>' + age + '</p>';
html +='</div>'



// es6
const name = 'zhangsan', age = 20;
const html = `
　　<div>
　　　　<p>${name}</p>
　　　　<p>${age}</p>
　　</div>
`;

A characteristic anti quotes, introducing a $ {variable}, the code read

 

3, deconstruction assignment

// JS
var obj = {a:100, b:200}
var a = obj.a;
var b = obj.b;


var arr = ['xxx', 'yyy', 'zzz'];
var x = arr[0];


//ES6
const obj = {a:10, b:20, c:30};
const {a, c} = obj;
console.log(a);
console.log(c);


const arr = ['xxx', 'yyy', 'zzz'];
const [x, y, z] = arr;
console.log(x);
console.log(y);
console.log(z);

4, block-level scope

js no block-level scope, will be buried pit

// JS
var obj = {a:100, b:200}
for (var item in obj){
　　console.log(item);
}
console.log(item) // b


// ES6
const obj = {a:100, b:200}
for(let item in obj){
　　console.log(item);
}
console.log(item);// undefined

 

5, the default function arguments

//JS
function fn(a,b){
　　if (b == null) {
　　　　b = 0;
　　}
}

//ES6
function fn(a, b=0){
 
}

 

6, arrows function

//JS
var arr = [1, 2, 3, 4, 5];
arr.map(function(item){
　　return item + 1;
})


//ES6
const arr = [1, 2, 3, 4, 5];
arr.map(item => item +1);



function fn(){
　　console.log('real', this); // {a:100}
　　var arr = [1, 2, 3];
　　arr.map(() => {
　　　　console.log(this); // {a:100}
　　})
　　arr.map(function(){
　　　　console.log(this)
　　})
}
fn.call({a: 100})