Web Design in a Nutshell, 3rd Edition

Statements

Each script we write consists of a series of statements . Statements can be terminated with a line break

first statement
    second statement

or with a semicolon (;)

first statement;second statement;

For readability, and to avoid potential statement termination problems, it is recommended that you use both:

first statement;second statement;

File Size Versus Readability

Using whitespace to improve readability does have one drawback: increased file size. Each whitespace character (tab, space, carriage return, or newline) is still a character in the document. With lots of whitespace (and comments , for that matter), a script file can get quite large.

To balance the need for whitespace and comments for legibility and the desire for fast downloads, many JavaScript developers keep two copies of every script they work on: a “working” copy with whitespace intact and a production version, which is “compressed” by stripping out all unnecessary whitespace and comments.