functions in JavaScript

In this article, we will learn about functions in JavaScript with the help of examples.

A function is a block that is designed to perform a specific task. JavaScript function executed when someone invokes it. Let’s see the syntax of the function.

Syntax of function:

// Syntax of function 
function functionName(){
    // function body
}

• In JavaScript, we declare functions using the function keyword.
• The basic rules for naming a function are similar to naming a variable. It’s better to give your function a meaningful name. For example, if a function is used to add two numbers, you might name the function add or addNumbers.
• The body of the function is written in {}.

For example:

// Example of function
// Print Recursive Minds using function
function printMsg(){
    console.log("Recursive Minds");
}

Invocation(calling) of function:

In the above program, we have created a function named printMsg. To use that function, we need to call it.

Here’s how you can call the above printMsg() function.

// function calling
printMsg();

Example 1: print message using function

// Example of function
// Print "Recursive Minds" using function
function printMsg(){
    console.log("Recursive Minds");
}

// function calling
printMsg();

Output:

Recursive Minds

function Parameters:

In JavaScript, we can also declare functions with parameters,  A parameter is a value that is passed to a function when the function is created.

Example 2: functions with parameter

// Example of function with parameter
function printMsg(name){
    console.log("Recursive Minds is started by " + name);
}
let name = "Amit Kumar";
// Calling of function
printMsg(name); // we are passing name to the function

Output:

Recursive Minds is started by Amit Kumar

In the above example, the printMsg is declared with name parameter. We have a name variable and “Amit Kumar” is in the name variable. When we called a function name is passed as an argument into the function.

NOTE: If a value is passed when declaring a function, it is called a parameter. And when the function is called, the passed value is called an argument.

Example 3: Program to add two numbers using the function

// Program to add two numbers using a function
// Function declaration
function addNums(num1, num2) {
    console.log(num1 + num2);
}

// calling functions
add(5,10); // Argument passing to function
add(8,2);

Output:

15
10

In the above example, the addNums function is used to find the sum of two numbers.

• The function is created with two parameters num1 and num2.
• The function is called two times using its name (addNums) and arguments are passed 5 and 10 in one and 8 and 2 in the second.

Here, you can see that we can call the function as many times as you can. You can create a function and use it multiple times with different arguments.

function return:

We can also return a value from the function and for that, we use the return keyword inside our function. When we return a value from a function, that value is returned to the call and we can store that value in a separate variable or print that value directly.

return denotes that function has ended. Any code after return is not executed.

Example 4: Program to return the sum of two numbers

// program to return sum of two numbers
// declaring a function
function addNums(num1, num2) {
    return num1 + num2;
}

// declaration of two numbers
let number1 = 50;
let number2 = 20;

// calling function
let sum = addNums(number1,number2);

// Print the sum
console.log("The sum is " + sum);

// We can also use 
console.log("The sum is " + addNums(20, 30));

Output:

70
50

function Expression:

In JavaScript, we can define the function as an expression. for example

// program to find the multiplication of two numbers
// function is declared inside the variable

let product = function (num1, num2) { 
     return num1 * num2 
};
console.log(product(4, 3));

// can be used as variable value for other variables
let y = product(3, 6);
console.log(y);

Output:

12
18

Thank you so much for reading

Happy Coding

For more details visit MDN Docs

Some other articles on JavaScript

• Introduction to JavaScript
• Variable in JavaScript
• JavaScript Data Types
• Let var const in JavaScript
• Operators in JavaScript
• JavaScript Conditionals
• for loop in JavaScript 
• while and do-while in JavaScript
• break and continue in JavaScript