Variables
var was used to declare variables in JavaScript.
To avoid errors and solving scoping issues we now use
let and const where let is a var like declaration and using const we make the variable immutable.
We need to use let and const as per our requirements.
Arrow function
Regular function in JavaScript
function myFunc () {
...
--function_body--
...
}
ES6 function in JavaScript
const myFunc = () => {
...
--function_body--
...
}
parenthesis can be removed if 1 parameter is passed and the return statement can be omitted if it is a one-liner
const myFunc = num => num * 5;
myFunc(5);
Export and Import
We use export default person to export a default parameter or function. Or we may export multiple functions from a single file
export const hello.
To import we follow the below syntax
To import default functions
import person from './person.js';
import prs from './person.js';
To import particular function from many export
import {hello} from './hello.js';
import {hello as Hi} from './hello.js';
import * as bundled from './hello.js';
Class
class Person{
name = "Raja"; //Property are variable
const call = () => { body } //Methods are functions
}
Usage:
const myPerson = new Person;
myPerson.call();
class Person {
constructor () {
this.name = "Sonu";
}
function printMyName () {
console.log(this.name);
}
}
Spread and Rest Operator
This is three dots ...
The spread operator is used to split up array or object elements
oldArr = [a, b, c]
const arr = [...oldArr, 1, 2]; // [a, b, c, 1, 2]
const oldObj = { name : 'Ashu'};
const obj = {
...oldObj,
age : 25
}
The rest operator is used to merge a list of arguments into an array
function sortArray (...args) {
return args.filter( item => item === 10);
}
sortArray(1,5,8,10);
Destructuring
To pick up particular items in an array and store them as variables
const numbers = [1, 2, 3];
[num1, , num2] = numbers;
console.log (num1, num2); // 1, 3
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