Sometimes you might want to make a note for yourself in your code. Comments can be helpful for remembering logic and terminology, and make your code easier to understand for other people.
// in front of the code or text. When you place these two slashes, all text to the right of them will be ignored, until the next line.
For example, here's a comment on the line above some code:
// checking type of hello worldconsole.log(typeof 'Hello world!');
You can even put comments on the same line as actual code:
console.log(typeof 'Hello world!'); // checking type of hello world