Functions in JavaScript

Updated October 12, 2023

What is the Functions of JavaScript

Subprograms execute specific tasks, and functions are one type of subprogram. Functions are considered objects and are executed when called or invoked. Within a program, you pass some value in a function. They return a value, but in JavaScript, the function will return undefined if you specify no return value in the function.

Types of function and their Syntax:

You can define functions in different ways. Like:

Function declaration: A keyword called “function” followed by the name of the function is used to create a function declaration. Using it allows you to hoist the function definition, enabling its use before definition.

Template of the same:

function name(parameters){
statement1
statement2….}
}

Function Expressions: You can use it to define a named function or an anonymous function. An anonymous function is nothing but a function that does not have a name.

While using Function expressions, you don’t hoist the definition of the function; therefore, it doesn’t allow it to be used before it is defined.

Template of the same:

let name = function (parameters){
statement1
statement2….}
}

In the above template, we have set an anonymous function object equal to a variable.

Arrow Function Expression: It shortens the syntax for writing function expressions. An Arrow function does not create a function value.

let name = (parameters) => {
statement1
statement2….}
}

Parameters vs. Arguments: 

While reading or learning about JavaScript, you would come across these terms, i.e., Parameters and Arguments. Though you may see them being used interchangeably, they are distinct and have a major difference.

Parameters: A function gets completed by the usage of Parameters. They are the names created in the function definition.

We can pass up to 255 parameters while defining a function. Write function arguments using simple brackets and separate them by commas.

Here’s a template with two parameters—a & b:

const a = true;
const b = false;
function two (a, b){
console.log(a, b);
}

On the other hand, Arguments are totally different from Parameters. Function arguments are the values received from each parameter when a function is executed (invoked).

In the above example, true & false are the two arguments.

Invoking a Function:

To execute a function, we call it or invoke it. To invoke a function, you write the function name and follow it with an open and closed simple bracket: ()

An Example of it:

Firstly, let’s define a function named tutorial and pass a parameter named name into it. While executing the function, it will log the parameter back to the console.

function tutorial(name){
console.log(name);
}

Now, let’s invoke or call this function.

tutorial('ram');
// ram

In the above example, I have called my function with the name ram.

For the cases where the function has no parameter: They can be invoked with an empty bracket, i.e. () For example:

function tutorial2(){
console.log('name2’);
}
tutorial2();
// name2

Function Return: 

JavaScript functions will return undefined until you define or specify them. An example to understand it better:

function tutorial(){};
tutorial();
// undefined

In the above example, we have called our function tutorial with no parameter, Therefore, it has returned undefined.

Now, we can use a return keyword followed by the value to return a value in the function. For example:

function tutorial(){
return true;
};
tutorial();
// true

In the above example, we have told the function to return true; this is another way to invoke a function.

⮚ One more important theory of the return statement is that it doesn’t let the function execute, and it stops it.

Let’s examine an example where a single function returns two statements.

function tutorial(){
return true;
return false;
};
tutorial();
// true

The first return statement has stopped the execution of the function. Therefore, it has returned only true(the first return statement) and has not executed the following return statements.

Function Objects:

∙ In general, Functions are nothing but objects.

∙ In JavaScript, an object is anything that is not a primitive type, i.e., which is not o a Boolean

o a Number

o a String

o Null or

o Undefined.

JavaScript allows us to pass a function as a parameter into another function. This shows the versatility of objects in JavaScript.

Higher-order Function: When a function returns a function or when a function is accepted by some other function as a parameter, it is called a higher-order function. For example: Array.prototype.filter and Array.prototype.map

Scope of JavaScript

JavaScript is an important technology to learn for new and modern developers. The importance of JavaScript technology is demonstrated by the fact that 94.5% of all websites are built using it.

Importance of JavaScript Functions

• It allows you to implement client-side scripts and server-server scripts. It simplifies the development of applications.
• It makes web page design responsive.
• It has an ample number of frameworks and libraries.
• It gets evolved with market needs.
• It makes the page dynamic.
• It gives a better user experience.
• You can use applications made in JavaScript offline. all you need to do is sync your data once the system goes offline.

Conclusion

JavaScript is an important tool in web development. This technology doesn’t seem to have an expiry date. Its specialty in providing responsiveness, the interaction between client and server, ample libraries and frameworks, etc., makes it unique. Its portability and efficiency make it a good choice for complex application development. Day by day, this technology is evolving at a good pace and therefore increasing its users.

This is a guide to Functions in JavaScript. Here we discuss the Introduction, Types of functions, and their Syntax and Importance of JavaScript. You may also have a look at the following articles to learn more –

1. JavaScript JSON to string
2. JavaScript hasOwnProperty()
3. JavaScript instanceof
4. JavaScript Object Notation