JavaScript Loop Performance Showdown

Which Type Of Loop Is Fastest In JavaScript?

Quick Summary: JavaScript, renowned for its versatility and potency, stands as a prominent programming language extensively employed in web development. In this discourse, we shall delve into the various loop types in JavaScript and conduct an in-depth analysis of their performance to ascertain which among them reigns as the swiftest.


Among the fundamental necessities in programming is executing a particular code block multiple times. Loops play a crucial role in this context, and all Javascript Frameworks offer a variety of loops, each with advantages and limitations. Explore the most suitable loop or iterator for your specific needs to avoid any inadvertent errors that could impact application performance.

The question is, Do you want to discover which loop or iteration best suits your needs? Various options are available in for loops, including for, for(reverse), for…of, for each, for…in, and for…await. The article presents one such debate, and we will discuss the fastest loop in JavaScript.

So, read and become one of the top Javascript Developers.

What is Loop In JavaScript?

In JavaScript, a loop is a Programming construct used to execute a block of code repeatedly. Additionally, there are different types of loops, including “for” Loops, “While” loops, and “do-while” loops. These allow you to iterate through arrays, perform actions based on conditions, and execute code multiple times. Furthermore, loops are essential for automating repetitive tasks and processing data efficiently in your programs.

Which is the fastest for loop?

Answer: for (reverse)

  • I’m surprised that for (reverse) is the fastest of all the for loops when I tested it locally. Here’s an example. Run for a loop through an array with over one million items.
  • Please note that console.time() results are highly dependent on your system configuration. Check out the accuracy here.
    • const million = 1000000;const arr = Array(million);console.time(‘⏳’);for (let i = arr.length; i > 0; i–) {} // for(reverse) :- 1.5msfor (let i = 0; i < arr.length; i++) {} // for          :- 1.6msarr.forEach(v => v)                     // foreach      :- 2.1msfor (const v of arr) {}                 // for…of     :- 11.7msconsole.timeEnd(‘⏳’);
  • The reverse for loop and the forward for loop takes almost the same amount of time. for(reverse) calculates a starting variable let i = arr.length only once, so there is a 0.1ms difference. After each increment in the forward for loop, it checks the condition i < arr.length. It will make no difference, ignore it.
  • On the other hand, foreach is a method of an array prototype. Comparatively to normal for loops, foreach, and for…of takes longer to iterate through the array.

expert Javascript developers

What loops are there, and when should you use them?

1. For loop (forward and reverse)

  • Everyone is probably familiar with this loop. If you need to repeat a block of code to fix counter times, you can use it for loops.
  • Traditionally, the for loop is the fastest, so you should always use them, right? Not necessarily. Performance is not the only factor. In general, code readability is more important, so choose the style that fits your application.

2. forEach

  • Upon receiving an array element, this method executes a callback function for each element. Furthermore, foreach’s callback function accepts the current value and the index.
  • foreach also allows you to use this keyword as an optional parameter within the callback function.
    • const things = [‘have’, ‘fun’, ‘coding’];const callbackFun = (item, idex) => {   console.log(`${item} – ${index}`);}things.foreach(callbackFun);o/p:- have – 0     fun – 1     coding – 2
  • In JavaScript, you cannot take advantage of short-circuiting if you use foreach. Let me introduce you to short-circuiting if you are unfamiliar with it. When we use a logical operator in JavaScript, like AND(&&), OR(||) we can bypass an iteration of a loop.

3. For…of

  • This for…of is standardized in ES6(ECMAScript 6). By using the for..of loop, you can iterate over an iterable object such as an array, map, set, string, etc. In addition, you can make the code more readable.
    • const arr = [3, 5, 7];const str = ‘hello’;for (let i of arr) {  console.log(i); // logs 3, 5, 7}for (let i of str) {  console.log(i); // logs ‘h’, ‘e’, ‘l’, ‘l’, ‘o’}
  • Note: For…of should never be reused on generators, even if for…of ends early. The generator is turned off after exiting the loop, and trying to repeat it produces no more results.

4. For…in

  • The for…in iterates over a variable that specifies all the enumerable properties of a given object. The for…in the statement will return the names of your user-defined properties along with the numeric indexes for every distinct property.
  • For this reason, it’s better to iterate over arrays with a for loop using a numeric index. Due to the fact that the for…in clause iterates over user-defined properties as well as the array elements, even if you modify the array object (by adding custom properties or methods).
    • const details = {firstName: ‘john’, lastName: ‘Doe’};let fullName = ”;for (let i in details) {   fullName += details[i] + ‘ ‘; // fullName: john doe}

5. For…in vs. for…of

The for…of and for…in differing primarily in the elements they iterate over. With for…in loops, you iterate over an object’s properties, whereas with for…of loops, you iterate over the values of an iterable object.

  • let arr= [4, 5, 6];for (let i in arr) {  console.log(i); // ‘0’, ‘1’, ‘2’}for (let i of arr) {  console.log(i); // ‘4’, ‘5’, ‘6’}

Guidelines for Enhancing Loop Efficiency

While the “for” loop is often the fastest, it’s crucial to consider that the performance difference between the loop types is not always substantial. In most cases, the choice of loop type won’t have a noticeable impact on performance, especially for small-scale applications.

However, optimizing the loop can be crucial for improving performance for large-scale applications or loops that involve a significant amount of processing. Presented below are several suggestions to enhance the efficiency of your loops.

  • When feasible, lessen the number of iterations.
  • Reduce or avoid doing needless calculations inside the loop.
  • Cache the loop length in a variable for “for” loops to prevent recomputation.
  • Use the “for…of” loop when iterating over arrays or iterable objects.
  • Employ loop unrolling when the quantity of iterations is predetermined.

Get started on optimizing your JavaScript code


  • The for loop is the fastest but poorly readable.
  • The foreach is fast, and iteration is controllable.
  • The for…of takes time, but it’s sweeter.
  • The for…in takes time, hence less convenient.

Choosing the fastest loop type in JavaScript depends on various factors, including the data set’s size and the code’s complexity within the loop. While the traditional “for” loop remains a reliable choice for most scenarios, modern JavaScript engines have improved the performance of other loop types, making them viable options in certain situations.

To achieve optimal performance, developers should carefully analyze their specific use cases and consider factors like code readability and maintainability. Developers can ensure efficient and performant JavaScript code by choosing the right loop type and following best practices.

Finally, a wise piece of advice for you. Prioritize readability. It is essential to maintain code readability when developing a complex structure at that time, but you should also pay attention to performance. Avoid adding unnecessary extras to your code as it can slow down your app.

Enjoy your coding time.😃


A variant of the while loop is the “do-while” loop. While loops may never execute, “do-while” loops always run at least once.

When the number of iterations is predetermined, the ‘for’ loop tends to exhibit greater speed. However, in some cases, modern JavaScript engines may optimize other loop types to achieve similar speeds.

The ‘for…of’ loop is explicitly designed for iterable objects such as arrays and strings, while you use the ‘for…in’ loop to iterate through an object’s properties.

To measure the start and end times of loop execution, you can utilize the method. When you calculate the difference between the start time and the end time, you will be able to obtain the execution time in milliseconds.

The “forEach” loop is particularly useful when you need to perform the same operation on each element of an array. Its concise syntax and ease of use make it a preferred choice for tasks that involve minimal computational overhead.