JavaScript Concepts - Revise your JavaScript concepts

If you're already familiar with JavaScript and want to revise JavaScript concepts then this repository can be helpful for you. We're using modern javascript (ES6) syntax. Kindly open an Issue if you notice anything wrong or Incorrect.

If it helps you then don't forget to give it a STAR ⭐️ and SHARE it with your JavaScript friends.

The Three Dots (...) Difference between Spread and Rest Operator

Spread Operator

const spreadOperator = (a, b, c) => a + b + c; // 2 + 4 + 6 = 12

const myArray = [2,4,6,1,9];

console.log(spreadOperator(...myArray)); // spreadOperator(2,4,6,1,9);

Rest Operator

const restOperator = (a, b, ...args) => {

// args [6,1,9]

let sum = 0;

args.forEach(arg => {

sum += arg; // 6 + 1 + 9 = 16

})

let product = a * b // 2 * 4 = 8

return [product, sum]; // [8, 16]

}

console.log(restOperator(2,4,6,1,9));

Asynchronous JavaScript

Callbacks

setTimeout(() => {
 console.log("3");
 setTimeout(() => {
  console.log("2");
  setTimeout(() => {
   console.log("1");
  }, 1000)
 }, 1000)
}, 1000)

Promises

const myPromise = new Promise((resolve, reject) => {
const randValue = Math.floor(Math.rand() * 2);
if(randValue === 0) resolve();
else reject();
})

myPromise.then(() => console.log("Success")).catch(() => console.log("Fail"));

Async Await

const myFunction = async () => {
try {
 const response = await fetch();
 const data = await response.data;
} catch(error) {
 console.error(error);
 }
}

Syntax Parser

Your code isn't magic. Someone else wrote a program to translate it for the computer

A program that reads your code and determines what it does and its grammar is valid.

Lexical Environment

where something sits physically in the code you write

Lexical means having to do with words or grammar. A lexical environment exists in programming language in which where you write something is important.

Execution Context

A wrapper to help manage the code that is running

There're a lot of lexical environments. Which one currently running is managed via execution contexts. It can contain things beyond what you've written in your code.

Conceptual Aside

Name/Value Pairs and Objects

Name Value Pair: A name which maps to a unique value. The name may be defined more than once, but only can have one value in any given context. That value may be more name/value pairs.

Object: A collection of name value pairs.

zainsadaqat/javascript