A comment is some text that is embedded within the script source text but is ignored by the interpreter. It is intended to provide guidance and documentation to the reader of the source code.
Comments can be contained completely on a single line or can span multiple lines.
A single line comment can contain any character except for a line terminator. The line terminator at the end of the single line comment is not part of the comment and must obey the rules of placement of line terminators in general. Multiple line comments are replaced by a single line terminator regardless of how many line terminators they actually contain. This means that a multiple line comment behaves syntactically as if it were a line terminator.
ECMA 262 edition 2 - section - 6
ECMA 262 edition 2 - section - 7.3
ECMA 262 edition 2 - section - 7.8.2
ECMA 262 edition 3 - section - 6
ECMA 262 edition 3 - section - 7.4