JavaScript identifiers are the name that we give to variables, objects, functions, arrays, classes, etc. We must use a unique name so as to identify them. We then use the identifier to refer to the variable, functions, etc elsewhere in the program. There are certain rules & restrictions that we must follow when we name an identifier.
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Example of Identifier
In the example below, the message is the name we have given to the variable. The variable holds the string “hello world”. Hence the message is Identifier.
1 2 3 4 | var message; message=”hello world”; |
In the following example, sayHello is the identifier.
1 2 3 4 5 | function sayHello(){ console.log('Hi') } |
JavaScript Identifiers Rules
When you name any identifier, you need to follow these rules.
- The identifier name must be unique within the scope.
- The first letter of an identifier should be a
- upper case letter
- Lower case letter
- underscore
- dollar sign
- The subsequent letters of an identifier can have
- upper case letter
- Lower case letter
- underscore
- dollar sign
- numeric digit
- We cannot use reserved keywords. You can find the list of keywords for here.
- They are case-sensitive. For Example,
sayHellois different fromSayHello - Cannot use spaces in a identifier name.
- Avoid using the JavaScript Reserved Keywords as identifier name
Example of Valid Identifiers
| Valid Identifier Names | ||
|---|---|---|
| empName | emp_name | _empName |
| result1 | $result | |
Example of Invalid Identifiers
| identifier | Reason |
|---|---|
| break | Because it is a Reserved keyword |
| emp name | spaces are not allowed |
| emp-name | – not allowed |
| 1result | cannot begin with a digit |
| emp@name | @ not allowed. only underscore and dollar allowed |
