JavaScript ignores spaces, tabs, and newlines that appear between "tokens" in programs, except those that are part of string constants. A "token" is a keyword, variable name, number, function name, or some other place where you would obviously not want to insert a space or a line break. If you place a space or tab or newline within a token, you obviously break it up into two tokens--123 is a single numeric token and 12 3 contains two separate tokens (and constitutes a syntax error, incidentally).
Because you can use spaces, tabs, and newlines freely in your program (except in strings and tokens) you are free to format and indent your programs in a neat and consistent way that makes the code easy to read and understand.