2.1 KiB
Comments
As time goes on, scripts tend to become more complex. We can add comments to describe what the code does and why.
Comments can be put into any place of a script. They don't affect its execution because the engine simply ignores them.
One-line comments start with two forward slash characters //. The rest of the line is a comment.
Such comment may occupy a full line of its own or follow a statement.
Like here:
// This comment occupies a line of its own
console.log("Hello");
console.log("World"); // This comment follows the statement
For longer, descriptive comments that span multiple lines, we can use the /* ... */ syntax.
Multiline comments start with a forward slash and an asterisk /* and end with an asterisk and a forward slash */.
Like this:
/* An example with two messages.
This is a multiline comment.
*/
console.log("Hello");
console.log("World");
The content of comments is ignored, so if we wrap a piece of code into /* ... */, it won't execute.
It can be handy to temporarily disable ("comment out") a part of code:
/* Commenting out the code
console.log("Hello");
*/
console.log("World");
In most editors, a line of code can be commented out by pressing the `key:Ctrl+/` hotkey for a single-line comment and something like `key:Ctrl+Shift+/` -- for multiline comments (select a piece of code and press the hotkey).
For Mac, try `key:Cmd` instead of `key:Ctrl` and `key:Option` instead of `key:Shift`.
There may not be `/*...*/` inside another `/*...*/`.
Such code will die with an error:
```js run no-beautify
/*
/* nested comment leads to an error! */
*/
console.log( "World" );
```
Please, don't hesitate to comment your code.
Comments increase the overall code footprint, but that's not a problem at all. There are many tools which minify code before publishing to a production server. They remove comments, so they don't appear in the working scripts. Therefore, comments do not have negative effects on production at all.