JavaScript comments are annotations in the code that are completely ignored by the compiler. For example,
// display "Programiz" to the screen
console.log("Programiz");
Output
Programiz
Here, // display "Programiz" to the screen is a comment. As a result, it is ignored by the JavaScript engine.
Types of JavaScript Comments
In JavaScript, there are two ways to add comments to code:
//- Single-Line Comments/* */- Multiline Comments
Single Line Comments
In JavaScript, any line that starts with // is a single-line comment. For example,
name = "Jack";
// display name on the console
console.log("Hello " + name);
Here, // display name on the console is a single-line comment.
Note: You can also use single-line comments like this:
name = "Jack";
console.log("Hello " + name); // display name on the console
However, avoid using comments this way if they are long and descriptive.
Multiline Comments
In JavaScript, multiline comments allow you to add comments that can span more than one line. They start with /* and end with */. For example,
/* This is a multiline comment.
It can span several lines.
*/
let numberOfStudents = 50;
console.log(numberOfStudents);
Here, we have used a multiline comment that can span any number of lines.
Comments can be helpful if you want to remove an unwanted line of code that can still be useful in the future. Consider the program below:
console.log("Welcome to JavaScript programming.");
console.log("JavaScript is fun!");
Suppose the line console.log("JavaScript is fun!"); isn't required right now. But you know that you might change your mind in the future.
In this case, you can simply convert the unnecessary line into a comment instead of deleting it from your program.
This way, you can uncomment the code whenever you need to use it.
console.log("Welcome to JavaScript programming.");
// console.log("JavaScript is fun!");
Make Code Easier to Understand
As a JavaScript developer, you'll write code and also need to update code written by others.
If you write comments on your code, it will be easier for you to understand the code in the future. It will also be easier for your fellow developers to understand the code.
As a general rule of thumb, use comments to explain why you did something rather than how you did something.
Notes:
- Comments shouldn't be used for explaining poorly written code. Your code should always be well-structured and self-explanatory.
- Remember the shortcut for using comments; it can be extremely helpful. For most code editors, it's
Ctrl + /for Windows andCmd + /for Mac.