es6 function扩展

_log = console.log
//参数默认值
function log(x,y = 'world'){
_log(`${x} ${y}`);
}

log('hello') //hello world
log('hello', 'china') //hello china

function Point(x = 0, y = 0){
this.x = x;
this.y = y;
}

_log(new Point());

function add(x = 1){
let x = 2; //报错
const x = 3; //报错
}

//与解构解析配合
function foo({x, y=5}){
_log(x,y)
}

foo({}); //undefined , 5
foo({x:1}); //1 5
foo({x:1,y:10}); // 1 10
//foo() //报错

function fetch(url , {body='',method='GET',headers={} }){
console.log(method);
}

fetch('http://qq.com',{}); //GET
//fetch('http://qq.com'); //报错

function fetch(url , {body='',method='GET',headers={}} = {}){
console.log(method)
}
fetch('http:qq.com');

function m1({x=0,y=0}={}){
console.log(x,y)
}

function m2({x,y} = {x:0,y:0}){
console.log(x,y);
}
m1(); //[00]
m2(); //[0,0]
m1({}); //[0,0]
m2({}); //[undefined,undefined]

//函数参数默认值，尽量放在尾部
function foo2(x, y=2){}
console.log(foo2.length)
//函数的length属性返回没有默认值参数的和

//作用域
var x = 1
function f(y=x){
console.log(y);
}
f(2);//2

/*function f2(y=x2){
let x2 = 2;
console.log(y); //报错
}
f2();
*/

let foo = 'outer'
function bar(func = x=> foo){
let foo = 'inner';
console.log(func());
}

bar()

//rest arguments
function add(...values){
var sum = 0;
for(let val of values){
sum += val;
}

return sum;
}

add(1,2,3,4,5)


 

 rest 参数

function sum(...values){
  let sum = 0;
  for(var i = 0; i < values.length; i++){
    sum += values[i];
  }
  return sum
}

排序

const sortNumbers = (...numbers)=>numbers.sort()

扩展运算符

console.log(...[1,2,3] + 6)
//1 , 2 , 3 6

function push(array, ...items){
array.push(...items)
}
var arr = [1,2,3]
push(arr, 4,5,6);
console.log(arr); //[1,2,3,4,5,6]

//代替es6
function f(x,y,z){}

var args = [0,1,2];

f.apply(null ,args);  //es5

f(...arg);//es6

var arr1 = [0,1,2]
var arr2 = [3,4,5]
Array.prototype.push.apply(arr1, arr2)  //es5

arr.push(...arr2)//es6

//数组的合并
var arr1 = ['a', 'b'];
var arr2 = ['c'];
var arr3 = ['d', 'e'];

arr.concat(arr2,arr3);  //es5
[...arr1,...arr2,...arr3] //es6

let list = [1,2,3,4,5,6];
//let a = list[0],
//    rest = list.slice(1);    //es5

//es6
[a, ...rest] = list;

const [first, ...rest] = ['foo']
//first 'foo'
//rest []

var go = function*(){
  yield 1;
  yield 2;
  yield 3;
}

[...go()]

function foo(){}
foo.bind({}).name; //"bound foo"

(function(){}).bind({}).name  //"bound "