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What are Identifiers in JavaScript?
April 30, 2020

An identifier is simply a name.

An identifier is a sequence of characters in the code that identifies a variable, function, or property.

In JavaScript, identifiers are used to name variables and functions and to provide labels for certain loops in JavaScript code.

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.

Digits are not allowed as the first character so that JavaScript can easily distinguish identifiers from numbers.

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.

Note, however, that JavaScript allows identifiers to contain letters and digits from the entire Unicode character set. This allows programmers to use variable names from non-English languages and also to use mathematical symbols:


var sí = true;
var π = 3.14;

Like any language, JavaScript reserves certain identifiers for use by the language itself. These “reserved words” cannot be used as regular identifiers.

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.

Sources

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