In JavaScript , identifiers can contain Unicode letters, $ , _ , and digits (0-9), but may not start with a digit. An identifier differs from a string in that a string is data, while an identifier is part of the code. In JavaScript, there is no way to convert identifiers to strings, but sometimes it is possible to parse strings into identifiers.

In CSS , there are two identifier data types: <custom-ident > and <dashed-ident > . The CSS <ident > can start with a digit and can contain almost any character, but non-letter/digit ASCII characters such as " , \ , and * need to be escaped. Emojis, which are valid as identifiers, do not need to be escaped.