Developers spend SO MUCH more time reading code than writing it. This is true even with your own code. As a favor to yourself and whoever will need to use, maintain, or further develop your code, please learn to write readable code.

Lesson Overview

This section contains a general overview of topics that you will learn in this lesson.

  • Know how to distinguish hard to read code from easy to read code.
  • Use programming principles to make your code cleaner.
  • Write good comments.

Writing Clean Code

Consider the following two snippets of JavaScript:

This is ugly and hard to read code:

const x =
function(z) {
let w = 0;z.forEach(
     w += q;
});return w;

x([2, 2, 2]);

Now, this is clean and easy to read code:

const sumArray = function(array) {
  let sum = 0;
  array.forEach(function(number) {
    sum += number;
  return sum;

sumArray([2, 2, 2]);

Believe it or not, both of those functions do the exact same thing (in the exact same way!), and both of them are perfectly valid code, but obviously the second one is much easier to follow. Imagine you’re working on a project with someone else and they’ve written the first function… how long is it going to take you to figure out what’s going on there so you can do your work? Imagine you’re working on a project all by yourself and YOU wrote the first function a week or two ago… chances are good that you aren’t going to remember exactly what you were up to there and it’s still going to take you a good while to figure it all out again.

The second one, however, is much easier to follow. Even if you don’t know exactly what everything in the code is doing, things are named clearly enough that you could guess, and the indentation is consistent enough that it’s easy to parse the different parts of the function.

There are many different opinions on what constitutes great JavaScript code. The most important thing is just that you’re consistent. The war between coders that use tabs and coders that use spaces to indent their code is so engrained that it’s essentially a joke by now, but it doesn’t really matter as long as you’re consistent.

Rules of Thumb

  1. Indentation: It doesn’t really matter what style of indentation you use. Various JS style-guides recommend different options, and one is not really superior to the other. What is important, however, is consistency. In our examples we will use 2 spaces for indentation.

  2. Semicolons: Semicolons are mostly optional in JavaScript because the JS compiler will automatically insert them if they are omitted. This functionality CAN break in certain situations leading to bugs in your code so it is better to get used to adding semi-colons. Just do it!

  3. Line length: Again, different style guides will recommend different options for this one, but just about ALL of them suggest limiting the length of each line of code. This rule is not quite as strict as some of the others, but as a general rule, your code will be easier to read if you manually break lines that are longer than about 80 characters. Many code editors have a line in the display to show when you have crossed this threshold. When manually breaking lines, you should try to break immediately after an operator or comma. Then, there are a few ways to format continuation lines. For example, you can:

    • indent continuation lines by one level,
    • vertically align continuation lines with the first variable,
    • or some other format entirely. The rules aren’t set in stone and vary from work environment to work environment, but remember to be consistent.
    // One possible format
    let reallyReallyLongLine =
      something +
      somethingElse +
      anotherThing +
      howManyTacos +
    // Another possible format
    let anotherReallyReallyLongLine = something + somethingElse + anotherThing +
                                      howManyTacos + oneMoreReallyLongThing;

  4. Naming Things: Names for functions and variables should be descriptive. Always use camelCase. To keep things consistent and easy to read, variables should always begin with a noun or an adjective (that is, a noun phrase) and functions with a verb. It is ok to use single characters as variable names in the context of a loop or a callback function, but not elsewhere.

    // Good
    const numberOfThings = 10;
    const myName = "Thor";
    const selected = true;
    // Bad (these start with verbs, could be confused for functions)
    const getCount = 10;
    const isSelected = true;
    // Good
    function getCount() {
      return numberOfThings;
    // Bad (it's a noun)
    function myName() {
      return "Thor";


  1. This list of clean-code tips.
  2. This article, and this one too about the role of comments in your code.

Knowledge Check

This section contains questions for you to check your understanding of this lesson on your own. If you’re having trouble answering a question, click it and review the material it links to.

Additional Resources

This section contains helpful links to related content. It isn’t required, so consider it supplemental.

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