What is a function?

 

A function is a block of code that performs a specific task. Suppose you need to create a counter. You can create two functions to solve this problem:

 

-a function to add to the counter

-a function to subtract from the counter

 

By breaking down a complex problem into smaller chunks, you can make your program more understandable and reusable.

 

javaScript also has a huge number of inbuilt functions. For example, Math.sqrt() is a function to calculate the square root of a number.

 

In this tutorial you will learn how to create your own defined function.

 

Declaring a function

 

The syntax to declare a function is:

function nameOfFunction () {
    // function body   
}

 

1.A function is declared using the function keyword

2.A function's name should follow the same principles as a variable's name. Giving your function a name that describes what it does is always a good idea.For example, if a function is used to add two numbers, you could name the function addor addNumbers.

3.The body of function is written within {}.

For example,

function greating(){
console.log("Hello there");
}

 

Calling a Function

In the above program, we have declared a function named greeting(). To use that function, we need to call it. Here's how you can call the above greeting() function.

// function call
greeting();

 

Example 1:

// program to print a text
// declaring a function
function greeting() {
    console.log("Hello there!");
}

// calling the function
greeting();

Output

Hello there!

 

Function Parameters

The declaration of a function can additionally include a set of parameters. When defining a function, a parameter is a value that is passed in.

 

Example 2: Function with Parameters

console.log("Enter a name:")
// program to print the text
// declaring a function
function greeting(name) {
    console.log("Hello " + name + ":)");
}

// calling function
greeting(name);

Output

Enter a name: Simon
Hello Simon :)

 

In the above function, it is declared with the paremeter name.when the function is called, an argument is passed into the function.

 

 

A function can have more than one paremeter :

// program to add two numbers using a function
// declaring a function
function add(a, b) {
    console.log(a + b);
}

// calling functions
add(3,4);
add(2,9);

 

Output

7
11

 

In the example above, the sum of two numbers is calculated using the add function.

 

 

Function Return

To return the value of a function call, use the return statement.

 

The return statement signals the end of the function. After return ,any code is not performed.

 

The function returns a undefined value if nothing is returned.

 

Example 4: Sum of Two Numbers

// program to add two numbers
// declaring a function
function add(a, b) {
    return a + b;
}

// take input from the user
let number1 = parseFloat(prompt("Enter first number: "));
let number2 = parseFloat(prompt("Enter second number: "));

// calling function
let result = add(number1,number2);

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

 

The prompt keyword enable the your browser or command line to place a request to the user, which in this case it you

 

Output

Enter first number: 3.4
Enter second number: 4
The sum is 7.4

 

In the above program, the sum of the numbers is returned by the function using the return  statement. And that value is stored in the result variable, and then printed out.

 

Benefits of Using a Function

-The use of functions allows the code to be reused. It is possible to declare it once and then utilize it several times.

-Each little task is split into a function, making the program easy to follow.

-Function increases readability.