10/18 奇妙之旅

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微信号 forjs_org

今天是周六，上午温习一下es6的用法。

destructuring

let [,x,y] = [1,3,2];

let {a,b,c} = {a:3,b:6,c:9};

let {a:a1,b,c:{h:h}} = {a:3,b:6,  c:{h:9}  }; // {a1,b,h}

function test ({a,b,c}){
    return a;
}
test({a:12,b:3:c:5}) // 12

Defualt parameter values

function test(url="forjs.org" , {name = "leo" , age}){
    // ...
}

Rest parameters

function test(...nums){
    nums.forEach(function(n){
        ...
    })
}

Spread Operator

function test(x,y,z){
    return x + y+z;
}

var arr = [1,2,3];
test(...arr) // 6

Template Literals

var sub = "book";
let url = `http://forjs.org/${sub}`

function test(str,...values){

}

let x=1,y=3;

var result = test `${x} + ${y} is ${x+y}`

// str = [""," + ", " is ", ""]
// values = [1,3,4]

Arrow Function

let add = (x,y) => x + y;

//or

let add = (x,y) => {
    return x + y;
}

let sum = 0,numbers = [1,2,3,4];

numbers.forEach(n => sum += n);
// 如果两个参数可以 (n,m) => sum + n +m ;

Iterables and Iterators

next()

{value:xxx , done:true/false}

var numbers = [1,2,23,3,2];

// create a iterator
let iterator = numbers.values();

let next = iterator.next(); // {value :1 , done : false}

for of

for of 使用的是 iterator技术支持！, 必须实现 iterator 方法，得到 iterator对象。

var numbers = [1,2,23,3,2];
for(let n of numbers){
   console.log(n);
}
// 1,2,23,3,2

不明白的写法

class User{ Symbol.iterator{ // why

} }

Generators

let numbers = function *(){
    yield 1;
    yeild 2;
}


var iterator = numbers();

// ... ...

特殊写法

clsss User{

    *iterator(){ // generator 写法
        yield 12;
    }
}

Comprehensions 解析

var numbers = [for(n of [1,2,3]) n * n];
// [1,4,9]

var numbers = (for(n of [1,2,3]) n * n); // ?

yield [if(true) 12 ] // yield 12
yield* [12,14]  // yield 12 ; yield 14;

Arrays

var match = [1,2,3,10].find(item => item > 8);
var arr = ...

arr.findInex(item => item > 3)

arr.fill("a")

arr.fill("a",2,3)

// [1,2,3,4]
arr.copyWithin(2,0,1); // 1,2,1,4

var arr = new Array(1,2,3); // [1,2,3]

var ofAry = Array.of(3) // [3]


var arrayLink = document.querySelectorAll("div");
var fromArray = Array.from(arrayLink); // -> Array type.


var entries = arr.entries();
var r = entries.next().value; // [0,"Joe"]

解构

var [x,,y] = [12,11,15];

console.log(x,y);

拓展参数

let test(p1,p2,p3) => console.log(`Hello ${p1} ${p2} ${p3}`);

var ps = [11,22,33];
test(...ps); // 原始使用 ps.apply(null,ps);