JS Tutorials
JS Introduction
JS Syntax
JS Comments
JS Variables
JS Operators
JS Data Types
JS Functions
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JS Numbers
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JS Functions
Function Definition
Function Parameters
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Function ClosuresJS Classes
Class Intro
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JS Aysnc
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JS Prmosies
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JavaScript Comments
JavaScript comments can be used to explain JavaScript code, and to make it more readable.
JavaScript comments can also be used to prevent execution, when testing alternative code.
Single Line Comments
Single line comments start with //.
Any text between // and the end of the line will be ignored
by JavaScript
(will not be executed).
This example uses a single-line comment before each code line:
Example
//
Change heading:
document.getElementById("myH").innerHTML = "My First Page";
// Change
paragraph:
document.getElementById("myP").innerHTML = "My first paragraph.";
This example uses a single line comment at the end of each line to explain the code:
Example
let x = 5;
// Declare x, give it the value of
5
let y = x + 2; // Declare y, give it the value of x +
2
Multi-line Comments
Multi-line comments start with /* and end with */.
Any text between /* and */
will be ignored by JavaScript.
This example uses a multi-line comment (a comment block) to explain the code:
Example
/*
The code below will change
the heading with id = "myH"
and the paragraph with id = "myP"
in my web page:
*/
document.getElementById("myH").innerHTML = "My First Page";
document.getElementById("myP").innerHTML = "My first paragraph.";
It is most common to use single line comments.
Block comments are often
used for formal documentation.