Comments

One-line comments start with the two forward slash characters //.

Multiline comments start with a forward slash and an asterisk /* and end with an asterisk and a forward slash */.

// This comment occupies a line of its own
alert('Hello');

alert('World'); // This comment follows the statement

/* An example with two messages.
This is a multiline comment.
*/
alert('Hello');
alert('World');

The content of comments is ignored, so if we put code inside /* … */ it won’t execute. Sometimes it comes in handy to temporarily disable a part of code:

/* Commenting out the code
alert('Hello');
*/
alert('World');