What are Looping Structures in Javascript?

February 13,2021 - 5 min read
What are Looping Structures in Javascript?

The market as well as the technology stack for the IT industry has significantly changed. There is a remarkable increase and improvement in the number of frameworks, libraries, tools and languages that are used to build technological applications. Javascript is one such example. It is a language that has emerged as one of the most popular languages of the IT industry.

If you are even distantly related from the world of technology then you would know that Javascript is a prominent language that offers a variety of features and makes it easier for developers to make user-friendly, interactive applications. Therefore, the job market for Javascript developers has also become competition.

Brendan Eich founded Javascript back in 1995 when it was initially used for creating interactive web pages. Javascript, an event-driven, functional and imperative language is popularly used to add dynamic effects on web pages like rollover, rollout and other interesting features.

Basically, Javascript is a scripting language that is capable of adding complex features on webpages. The contributions of Javascript are varied, for example, a scrolling video jukebox, animated graphics or simply a dynamic update on your website are all with the help of Javascript in coordination with HTML and CSS.

We have talked about Javascript as a client side language. However, apart from adding features to the client side, Javascript is also a very popular client side language.

Javascript was initially designed to run on browsers. Every browser has a Javascript engine, for example, Chrome’s v8 engine. Ryan Dahl created Node which is basically a C++ program that allows you to run javascript code outside of a browser. Hence, Javascript has now diversified as a server side language that can develop a wide range of applications.

In today’s time, Javascript can be used at the server-side also. The framework used for server-side web development is Nodejs. Apart from server and client side applications, Javascript can be used to make stand-alone desktop applications also.

There are various frameworks that are used to create dynamic web as well as mobile applications. For example, React is popular for creating dynamic web applications while React native is dedicated for mobile applications only. Angular is another framework that can be used with Javascript to make dynamic web applications.

Javascript is an important language with varied uses in different domains in the world of technology. Big companies like Netflix, Uber, Paypal and others use Javascript to create dynamic webpages that are fast, user-friendly and secure.

In today’s blog, we are going to talk about the different looping structures in Javascript. Looping is an important concept in any computing language as Javascript is no different. In today’s blog, we are going to talk about the most common types of loops in Javascript. Let’s get started!

Loops in Javascript

Loops in JavaScript are used to iterate a particular piece of code. They are used to perform repeated tasks based on a condition that typically returns true or false upon analysing. The loops stops when the condition is met or it returns false. Looping structures are am important part of programming.

The main loops in Javascript are ‘for’, ‘while’, ‘do while’ and ‘for-in’ loops. Using loops makes the code compact and easy to read. It can be used with any data structure; however, it is mostly used with arrays. In this blog, we explain the most commonly used loops in Javascript. Let’s get started!

  1. For Loop

    The For loop in Javascript is used to tun before the first execution on the loop. The syntax of for loop in Javascript is -
    for ([initialization]; [condition]; [final-expression]) {
    // body of the loop to be written here.
    The syntax consists of three parts along with the body of the loop. The first part is initialisation which is run before the first iteration of the loop. Initialisation is commonly used to create counters. The scope of variables created here is only inside the loop and hence once the execution of the loop is terminated, the variables created are destroyed.

    The second part is condition which is checked prior to the execution of every iteration. The execution of the loop depends on whether the condition is evaluated to be true or false. The loop terminates if the condition is evaluated to be false.

    The final expression is run after every iteration and is usually used to increment or decrement a counter.

    The body of the loop contains the code that needs to be executed a certain number of times. The code inside the body of the loop is executed till the loop runs, however, if you want to stop the lop before the condition is evaluated id false, you can use a break statement to exit the loop.

    This was the basic concept along with the syntax of for loops. It is time we look at some of the common pitfalls of for loop and general guidelines to keep in mind while executing the for loop in Javascript.

    A common problem faced in loops are that sometimes the conditions are so that they exceed the bounds of an array or any other static data structure. When traversing over an array many times, it is common to exceed the limits of the array, for example, in an array of 3 elements, if you want to reference the 4th element, it will cause an error because the bounds of the array will be exceeded. However, the condition can be easily fixed with the help of certain functions being specified in the condition like i < arr.length or i <= arr.length – 1.

    In Javascript, there are various types of for loops. In the next segment, we are going to talk about the many types of loops. The first one we are going to talk about is the ‘for...in’ loop.

    In Javascript, the ‘for...in’ statement iterates over the enumerable properties of an object, in arbitrary order. The statement is executed for each distinct property. The syntax of the ‘for...in’ loop is -

    for (variable in object) {

    //body of the loop


    The next in line is the ‘for...of’ loop which creates a loop iterating over the objects like Array, Map, Set, Arguments object among others. It invokes a custom iteration hook with statements that is executed for the value of each distinct property.

    In this segment, we have discussed the different types of for looping in Javascript. Next, we are going to talk about ‘while’ loop in Javascript. Let’s get started!

  2. While Loop

    While loop in Javascript starts by evaluating the condition and if the condition is true, the body of the code is executed and not if otherwise and the loop ends. The syntax for while loop is –

    while (condition) {

    Body of the loop;}

    The body of the loop contains code that is executed as long as the condition of the while loop evaluates to be true. In Javascript, ‘while’ loop contains condition that are Boolean expression which is evaluated before each iteration through the loop. If the condition evaluates to true, the body of the loop is executed. There is one example of while loop given below -

    var k = 1;
    while (k < 10)
    k++; //

    The output of the code mentioned above will be numbers from 1 to 6.

    The next variation of the while loop is the Do...while loop. The ‘do...while’ loop is very much like the loop, however, the difference between the two is that in ‘do while’ loop, the condition is checked at the end of the loop and in while loop, the condition is checked in the beginning or before the first loop is executed.

    The syntax for ‘do...while’ loop is a-beginner’s-guide-to-algorithmic-thinking do {
    //body of the loop.
    } while (condition);

    The body of the loop that contains the code is executed at least once because the condition or Boolean expression is evaluated at the end of the first iteration. The conditions are then checked and each time the condition evaluates to true, the code in the body of the loop is executed. These conditions, as mentioned above, are Boolean expression.

    These were some of the Javascript looping structures that are most commonly used while coding and developing user friendly and interactive applications. These loops are used to execute a particular code or traverse a particular data structure. I hope the concept of looping structures is now clear in your mind. However, if you still have doubts and queries regarding Javascript looping structures, we would be more than happy to help you. It’s important to get these basic concepts cleared before you advance to developing high level, advanced and real- life projects. We wish you all the best for your journey in technology.

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