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.

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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 line, to explain the code:

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

var x = 5;      // Declare x, give it the value of 5var y = x + 2;  // Declare y, give it the value of x + 2

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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.";

Source: http://www.w3schools.com/js/js_comments.asp