[JavaScript] ES6语法小结
2016-05-05 本文已影响259人
何幻
1. var versus let/const
let snack='Meow Mix';
function getFood(food){
if(food){
let snack='Friskies';
return snack;
}
return snack;
}
getFood(false); //'Meow Mix'
2. Replacing IIFEs with Blocks
{
let food='Meow Mix';
}
food; //Reference Error
3. Arrow Functions
function Persion(name){
this.name=name;
}
Person.prototype.prefixName=function(arr){
return arr.map(character=>this.name+character);
};
4. Strings
// ---- 4.1 .includes()
const string='food';
const substring='foo';
string.includes(substring); //true
// ---- 4.2 .repeat()
'meow'.repeat(3); //'meowmeowmeow'
5. Template Literals
// ---- 5.1 Special characters
let text=`This string contains "double quotes" which don't need to be escaped anymore.`;
// ---- 5.2 interpolation
const name='Tiger';
const age=13;
`My cat is named ${name} and is ${age} years old.`;
// ---- 5.3 Preserve new line
let text=(`cat
dog
nickelodeon`);
// ---- 5.4 Accept expressions
let today=new Date();
let text=`The time and date is ${today.toLocalString()}`;
6. Destructuring
// ---- 6.1 Destructuring Arrays
let [a,b,c,d]=[1,2,3,4];
a; //1
b; //2
// ---- 6.2 Destructuring Objects
let luke={occupation:'jedi',father:'anakin'};
let {occupation,father}=luke;
occupation; //'jedi'
father; //'anakin'
7. Modules
// ---- 7.1 Named Exports
export let name='David';
export let age=25;
export function sumTwo(a,b){
return a+b;
}
// ---- 7.2 Export a list
function sumTwo(a,b){
return a+b;
}
function sumThree(a,b,c){
return a+b+c;
}
export {sumTwo,sumThree};
// ---- 7.3 Export default bindings
function sumTwo(a,b){
return a+b;
}
function sumThree(a,b,c){
return a+b+c;
}
let api={
sumTwo,
sumThree
};
export default api; //export {api as default};
// ---- 7.4 Import an entire file
import 'underscore';
// ---- 7.5 Named imports
import {sumTwo,sumThree} from 'math/addtion';
// ---- 7.6 Rename the named imports
import {
sumTwo as addTwoNumbers,
sumThree as addThreeNumbers
} from 'math/addtion';
// ---- 7.7 Import all the things
import * as until from 'math/addtion';
const {sumTwo,sumThree}=util;
// ---- 7.8 Import from the default binding
import api from 'math/addtion'; //import {default as api} from 'math/addtion';
// ---- 7.9 Mix default
export {foo as default,foo1,foo2};
import foo,{foo1,foo2} from 'foos';
8. Parameters
// ---- 8.1 Default parameters
function addTwoNumbers(x=0,y=0){
return x+y;
}
addTwoNumbers(2,4); //6
addTwoNumbers(2); //2
addTwoNumbers(); //0
// ---- 8.2 Rest parameters
function logArguments(...args){
for(let arg of args){
console.log(arg);
}
}
// ---- 8.3 Option paramters
function initializeCanvas({height=600,width=400,lineStroke='black'}){
//height,width,lineStroke
}
function initializeCanvas({height=600,width=400,lineStroke='black'}={}){
//height,width,lineStroke
}
// ---- 8.4 Spread operator
Math.max(...[-1,100,9001,-32]);
let cities=['San Francisco','Los Angeles'];
let places=['Miami',...cities,'Chicago'];
9. Classes
class Person{
constructor(name,age,gender){
this.name=name;
this.age=age;
this.gender=gender;
}
incrementAge(){
this.age++;
}
}
class Personal extends Person{
constructor(name,age,gender,occupation,hobby){
super(name,age,gender);
this.occupation=occupation;
this.hobby=hobby;
}
incrementAge(){
super.incrementAge();
this.age+=20;
}
}
10. Symbols
// ---- 10.1 Non-global symbol
const refreshComponent=Symbol();
React.Component.prototype[refreshComponent]=()=>{
//
};
Symbol('foo')===Symbol('foo'); //false
// ---- 10.2 Global symbol
Symbol.for('foo')===Symbol('foo'); //false
Symbol.for('foo')===Symbol.for('foo'); //true
11. Maps
// ---- 11.1 .set(),.get(),.has()
let map=new Map();
map.set('name','david');
map.get('name'); //david
map.has('name'); //true
// ---- 11.2 Any types as key
let map=new Map([
['name','david'],
[true,'false'],
[1,'one'],
[{},'object'],
[function(){},'function']
]);
for(let key of map.keys()){
typeof key; //string,boolean,number,object,function
}
for(let [key,value] of map.entries()){
key,value;
}
12. WeakMaps
// ---- 12.1 No property name
let _age=new WeakMap();
class Person{
constructor(age){
_age.set(this,age);
}
incrementAge(){
let age=_age.get(this)+1;
_age.set(this,age);
}
}
const person=new Person();
Reflect.ownKeys(person); //[]
// ---- 12.2 Auto destroy
let map=new WeakMap();
let el=document.getElementById('someElement');
map.set(el,'reference');
map.get(el); //'reference'
el.parentNode.removeChild(el);
el=null;
map.get(el); //undefined
13. Promise
// ---- 13.1 Error handler
new Promise((resolve,reject)=>{
reject('Failed to fulfill Promise');
}).catch(reason=>console.log(reason));
new Promise((resolve,reject)=>{
throw 'Exception happens';
}).catch(error=>console.log(error));
// ---- 13.2 Parallel promise
let urls=[
'/api/commits',
'/api/issues/completed'
];
let promises=urls.map(url=>{
return new Promise((resolve,reject)=>{
$.ajax({url:url}).done(data=>resolve(data));
});
});
Promise.all(promises)
.then(results=>{
//
});
14. Generators
// ---- 14.1 yield
function* sillyGenerator(){
yield 1;
yield 2;
return 3;
}
let gen=sillyGenerator();
gen.next(); //{value:1,done:false}
gen.next(); //{value:2,done:false}
gen.next(); //{value:3,done,true}
// ---- 14.2 yield promise
function* getData(){
let entry1=yield request('some_api/item1');
let data1=JSON.parse(entry1);
let entry2=yield request('some_api/item2');
let data2=JSON.parse(entry2);
}
function request(url){
return new Promise((resolve,reject)=>{
getJSON(url,resolve);
});
}
function iterateGen(generator){
var gen=generator();
(function iterate(val){
let ret=gen.next();
if(!ret.done){
ret.value.then(iterate);
}
}());
}
15. Getter and Setter functions
var person={
firstName:'James',
lastName:'Bond',
get fullName(){
return this.firstName+' '+this.lastName;
},
set fullName(name){
let words=name.split(' ');
this.firstName=words[0];
this.lastName=words[1];
}
};
person.fullName; //James Bond
person.fullName='Bond 007';
person.fullName; //Bond 007
16. Object
// ---- 16.1 Variable as property
var foo='bar';
var baz={foo};
baz; //{foo:'bar'}
// ---- 16.2 Method
var obj={
method(){
//
}
};
// ---- 16.3 Generator
var obj={
*gen(){
//
}
};
// ---- 16.4 Return
function foo(x,y){
return {x,y};
}
// ---- 16.5 Export
export {sumTwo,sumThree};
// ---- 16.6 String as property name
var propKey='foo';
let obj={
[propKey]:true,
['a'+'bc']:123,
['h'+'ello'](){
//
}
};
17. Iterable/Iterator
let fib={
[Symbol.iterator](){
let pre=0,cur=1;
return {
next(){
[pre,cur]=[cur,pre+cur];
return {done:false,value:cur}
}
};
}
};
for(var n of fib){
if(n>10){
break;
}
console.log(n);
}
