JavaScript comments are used to explain the code to make it more readable. It can be used to prevent the execution of a section of code if necessary. JavaScript comments are ignored while the compiler executes the code.
Single Line Comments
In Javascript, single-line comments start with //. Any code written after // will be ignored by Javascript.
Example 1: This example illustrates the single-line comment using //.
Javascript
// A single line comment console.log("Hello Geeks!"); |
Hello Geeks!
Example 2: In this example, we will assign values to some variables and explain them with single-line comments.
Javascript
// Declaring a variable and assign value to itlet geek = 'Computer science portal';console.log(geek)// Perform operation of addition of two numberslet sum = 5 + 8console.log(sum) |
Computer science portal 13
Multi-line Comments
In Javascript, multi-line comments start with /* and end with */. Any text or code written between /* and */ will be ignored by JavaScript at the time of execution.
Example: This example illustrates the multi-line comment using /* … */
Javascript
/* It is multi line comment. It will not be displayed upon execution of this code */ console.log("Multiline comment in javascript"); |
Multiline comment in javascript
JavaScript Comments to Prevent Execution
We can use // or /*…*/ to change the JavaScript code execution using comments. JavaScript Comments are used to prevent code execution and are considered suitable for testing the code.
Example 1: JavaScript comments are used to prevent execution of selected code to locate problems of code or while testing new features. This example illustrates that commented code will never execute.
Javascript
function add() { let x = 10; let y = 20; let z = x + y; // console.log(x + y); console.log(z);}add(); |
Output: The sum is calculated but is only displayed once because the code to display the sum is written in a comment in the other line and will not be displayed.
30
Example 2: This example uses multi-line comments to prevent the execution of addition code and perform subtraction operations.
Javascript
function sub() { let x = 10; let y = 20; /* let z = x + y; console.log(z); */ let z = x - y; console.log(z);}sub(); |
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