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:

This example uses a single line comment at the end of each line to explain the code:

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:

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:

This example uses a comment block to prevent execution of multiple lines: