const
const myVar = 'value';myVar = 'value2'; // error
let
var myVar = 'value';
if( myVar ){
let myVar = 'value2';
console.log(myVar); // 'value2'
}
console.log(myVar); // 'value'
String Template
let myHtml = `<div>${myVar}</div>`; // ` -> back tick character
let myTemplate = `
<div>
<span>${var1}</span>
<span>${var2}</span>
</div>
`;
Default values
function myFunction(par='some value'){
// code
}
var defaultValue = 'value';
function MyFunction2(par=defaultValue){
// code
}
Arrow function
let add5 = par1 => par1+5;
let sum = (par1, par2) => par1 + par2;
let myFunc = (par1, par2) => {
if(par1<=0){
par1 = 1;
}
return par1*par2;
}
let myObj = {
myMeth: function(){
// code
}
myMeth2: function(){
setTimeout(function(){
this.myMeth(); // ERROR! function not preserve scope
}, 1000);
}
myMeth2: function(){
setTimeout( ()=>{
this.myMeth(); // scope is myObj
},1000);
}
}
Destructuring
let obj = {k1:v1, k2: v2};
let {k1, k2} = obj;
console.log(k1, k2);
let myFunc = ({k1}) => console.log(k1);
let arr = ['first', 'second', 'third'];
let [firstItem] = arr;
let [,, thirdItem] = arr;
Object Literal Ehancement
let var1 = value1;
let var2 = value2;//rest is array without first item
let obj = {var1, var2}; //obj= {var1:value1, var2:value2}
let myFunc = function(){
return this.var1;
};
let obj2 = {var1, var2, myFunc};
let obj3 = {
prop1,
prop2,
myMeth(){
//code
}
}
Spread Operator
let arr1 = [v1, v2, v3];
let arr2 = [v4, v5, v6];
let arr3 = [...arr1, ...arr2]; //arr3 = [v1, v2, v3, v4, v5, v6];
let [last] = arr.reverse(); //array altered
let [last] = [...arr].reverse();
let [first, ...rest] = arr; //rest is array without first item
let obj = {k1:v1, k2:v2};
let prop = value;
let obj2 = {...obj, prop};
Promise
const getUsers = count => new Promise(
(resolves, rejects) => {
const url = `http://myapi/user/?limit:${count}`;
const req = new XMLHttpRequest/(;
req.open('GET', url);
req.onload = () => req,status == 200 ?
resolves(JSON.parse(req.response)).results :
reject(Error(req.statusText));
req.onerror = (err) => reject(err);
req.send();
}
);
getUsers(10).then(
users=>console.log(users),
err => console.error(err)
);
getUsers(10)
.then(users=>console.log(users))
.catch(err=>console.log(err));
Class
class MyClass {
constructor(par1, par2){
// code
}
myMeth(){
// code
}
}
class MyClass2 extends MyClass{
constructor(par1, par2, par3){
super(par1, par2);
// code
}
myMeth2(){
// code
}
}
Module
Module -> file
file1.js
export const myFunc = (par1) => par1+5;
export const myFunc2 = (par2) => par2^2;
file2,js
export const default myVar = 5;
file3.js
import {myFunc, myFunct2} from "./file1";
import {myVar} from "./file2";
alias
import {myFunc as f1, myFunct2 as f2} from "./file1";
all
import * as f from "./file1"
NodeJS (Common js)
file1.js
module.exports = {myFunc, myFunct2};
file3.js
const {myFunc, MyFunc2} = require("./file1");
