JavaScript Comments
JavaScript, like most programming languages, provides developers ways to leave comments through the code. JavaScript comments can be used to:
- explain a block code
- make code more readable
- leave messages for other developers or yourself
- prevent execution, when testing or experiment with code
JavaScript has two forms of comments Single Line Comments and Multi-line Comments.
Single Line Comments
Single line comments start with // and continue until the end of the line. Any text following the // and before the end of the line will be ignored by JavaScript.
// The following line demonstrates how to log a message to the console
console.log('Hello, World!')
// The following line demonstrates how to log a warning to the console
console.warn('Take me to your leader!')
Single line comments can be used on the same line as code. These comments are referred to as inline comments.
const a = 3
const b = 5
const c = a + b // The value of c should be 8
Multi-line Comments
Multi-line comments, or block comments, start with /* and end with */
Any text between /* and */ will be ignored by JavaScript.
/*
The multiply function takes
two numbers and multiplies them together
and returns the product.
*/
function multiply (a, b) {
return a * b
}
NOTE
Multi-line comments are often used for formal documentation
Preventing Code Execution
Using comments to prevent code execution is an acceptable way to test and experiment with code.
Adding // in front of a line of code will prevent the line of code from executing.
// The following line demonstrates how to log a message to the console
console.log('Hello, World!')
// The following line demonstrates how to log a warning to the console
console.warn('Take me to your leader!')
// The following line will not be executed
// console.error('Resistance is futile!')