Functions in JavaScript

A function in JavaScript is similar to a procedure—a set of statements that performs a task or calculates a value, but for a procedure to qualify as a function, it should take some input and return an output where there is some obvious relationship between the input and the output.

Video Explanation​

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Functions Declaration​

Function Declarations also known as function statement or function definition consists of function keyword, function name, parameters separated by commas and function body enclosed by curly braces { /*function body*/ }

function printName(name) {
    return name;
}

In the example above, the function printName takes one parameter called name. The function body consist of one statement that returns the name.

Function Expressions​

Function expressions are a way to define a function as part of an expression. Unlike function declarations, which define a function with a name, function expressions can be anonymous (without a name) or named.

1. Anonymous Function Expression​

An anonymous function expression is a function that doesn't have a name. It can be assigned to a variable, passed as an argument to another function, or returned from another function.

const greet = function() {
    console.log("Hello!");
};

greet();

2. Named Function Expression​

A named function expression includes a name. This can be useful for recursion or for better debugging.

const greet = function sayHello() {
    console.log("Hello!");
};

greet();

3. IIFE (Immediately Invoked Function Expression)​

An IIFE is a function that runs as soon as it is defined. It’s often used to create a local scope.

(function() {
    console.log("This runs immediately!");
})();

Function Call​

Calling a function means executing the code defined within it. There are various ways to call a function.

const greet = function(name) {
    console.log("Hello ", name);
};

greet("World!"); //Output: Hello World!

The above example is calling a function with argument

const obj = {
    greet: function() {
        console.log("Hello from an object!");
    }
};

obj.greet(); // Output: Hello from an object!

The above example is calling a method of an object

const multiply = (x, y) => x * y;

console.log(multiply(2, 3)); // Output: 6

The above example is of calling an arrow function

More Resources:​

• MDN Web Docs: Functions
• W3Schools: JavaScript Functions