Talking about JavaScript function

What is Function in JavaScript?

In JavaScript, functions are defined with the 'function' keyword.

• There is an another way to define a function, called 'Arrow Function'.

Declaration a Function

Syntax

function firstFunction () { // Code here ... } 

Example

function firstFunction () { console.log('JavaScript function'); } firstFunction(); // JavaScript function 

Function Expressions

A function expression can be stored in a variable.
Syntax

let firstFunction = function () { // Code here ... } 

Example

let firstFunction = function () { return "JavaScript function"; } firstFunction(); // JavaScript function 

Arrow Function

Arrow function allows a short syntax for writing function expressions.

• We don't need the 'function' keyword, the 'return' keyword and the 'curly' brackets.

Syntax

let change = (argument1, argument2) => Code here ... ; 

Example:

let add = (x , y) => x + y; add(4, 6); // Output will 10 

Function Parameters

If you want to build a dynamic function then you have to use parameters.

• Parameters are like an input. Based on your input it gives you the output.

Syntax with example

function add(x, y) { return (x + y); } add(10, 5); // Output: 15, // Here, x is 10, y is 5. 

Default Parameters

If a function is called with missing arguments, the missing values are set to undefined.

• It is better to assign a default value to the parameter.

Syntax

function myFunction (argument1 = default value) { // Code here ... } 

Example

function sum (x = 1, y = 1) { return (x + y); } sum(4, 6); // here x is 4, y is 6 sum(4); // here x is 4 but y is 1 (default value) sum(); // here x is 1, y is 1