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(1)
// Change heading: document.getElementById("myH").innerHTML = "My First Page"; // Change paragraph: document.getElementById("myP").innerHTML = "My first paragraph.";
var x = 5; // Declare x, give it the value of 5 var 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(3)
/* 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.";
Using Comments to Prevent Execution
Using comments to prevent execution of code is suitable for code testing.
Adding //
in front of a code line changes the code lines from an executable line to a comment.
This example uses // to prevent execution of one of the code lines:
Example(4)
//document.getElementById("myH").innerHTML = "My First Page"; document.getElementById("myP").innerHTML = "My first paragraph.";
This example uses a comment block to prevent execution of multiple lines:
/* document.getElementById("myH").innerHTML = "My First Page"; document.getElementById("myP").innerHTML = "My first paragraph."; */
Complete Code For Different Types Of Comments Used In JavaScript.
<!DOCTYPE html> <html> <head> <title>Which Are The Different Types Of Comments Used In JavaScript</title> <meta charset="utf-8"> <meta name="viewport" content="width=device-width, initial-scale=1"> <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.4.1/css/bootstrap.min.css"> </head> <body> <div class="container"> <br> <br> <br> <div class="text-center"> <h1 id="color" style="color: tomato">Which Are The Different Types Of Comments Used In JavaScript</h1> </div> <br> <br> <br> <div class="col-md-2"></div> <div class="col-md-8"> <div class="well"> <h2 id="demo1"></h2> <h2 id="demo2"></h2> <h2 id="demo3"></h2> <h2 id="demo4"></h2> <h2 id="demo5"></h2> </div> </div> <div class="col-md-2"></div> <script> // Change heading: document.getElementById("demo1").innerHTML = "My First Page"; // Change paragraph: document.getElementById("demo2").innerHTML = "My first paragraph."; var x = 5; // Declare x, give it the value of 5 var y = x + 2; // Declare y, give it the value of x + 2 /* The code below will change the heading with id = "myH" and the paragraph with id = "myP" in my web page: */ document.getElementById("demo3").innerHTML = "My First Page"; document.getElementById("demo4").innerHTML = "My first paragraph."; //document.getElementById("myH").innerHTML = "My First Page"; document.getElementById("demo5").innerHTML = "My first paragraph."; /* document.getElementById("myH").innerHTML = "My First Page"; document.getElementById("myP").innerHTML = "My first paragraph."; */ </script> </div> </body> </html>