Javascript MOST Important Concepts everyone should know

Today we are going to talk about the most essential JavaScript Concepts

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Scope

Scope determines the accessibility of variables, objects, and functions.

In Javascript, a variable has 3 types of scope:

a. Block Scope
b. Function Scope
c. Global Scope

Hoisting
Hoisting in Javascript is a behavior in which a function or variable can be used before declaration.
In terms of the variable and constant keyword var is hoisted, and let and const do not allow hoisting.

Closures

A closure is a function that remembers the variables in its surrounding scope, even when the function is executed outside of that scope.

Code

function makeCounter() {
let count = 0;
return function() {
return count++;
};
}
let counter = makeCounter();
console.log(counter()); // 0
console.log(counter()); // 1
console.log(counter()); // 2

Callbacks

A callback is a function that is passed as an argument to another function and is executed after the first function is done.

Code

function add(a, b, callback) {
let result = a + b;
callback(result);
}

add(2, 3, function(result) {
console.log(result); // 5
});

Promises

A promise is a way to handle asynchronous operations in JavaScript. It represents a value that will be available in the future, either as a result or an error.

Code

let promise = new Promise(function(resolve, reject) {
setTimeout(function() {
resolve(“Hello, World!”);
}, 1000);
});

promise.then(function(value) {
console.log(value); // “Hello, World!”
});

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