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 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:
<!DOCTYPE html>
<html>
<body>
<h1 id="myH"></h1>
<p id="myP"></p>
<script>
// Change heading:
document.getElementById("myH").innerHTML = "JavaScript Comments";
// Change paragraph:
document.getElementById("myP").innerHTML = "My first paragraph.";
</script>
</body>
</html>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:
<!DOCTYPE html>
<html>
<body>
<h1 id="myH"></h1>
<p id="myP"></p>
<script>
/*
The code below will change
the heading with id = "myH"
and the paragraph with id = "myP"
*/
document.getElementById("myH").innerHTML = "JavaScript Comments";
document.getElementById("myP").innerHTML = "My first paragraph.";
</script>
</body>
</html>It is most common to use single line comments.
Block comments are often used for formal documentation.