An identifier is simply a name.
An identifier is a sequence of characters in the code that identifies a variable, function, or property.
Identifiers are case-sensitive and can contain Unicode letters, $, _, and digits (0-9), but may not start with a digit.
Subsequent characters can be letters, digits, underscores, or dollar signs.
These are all legal identifiers:
x variable_name y13 _dummy_var $string
For portability and ease of editing, it is common to use only ASCII letters and digits in identifiers.
var sí = true; var π = 3.14;