JavaScript Reserved Keywords
| Site: | Saylor Academy |
| Course: | PRDV401: Introduction to JavaScript I |
| Book: | JavaScript Reserved Keywords |
| Printed by: | Guest user |
| Date: | Wednesday, May 14, 2025, 8:06 AM |
Description
JavaScript statements begin with a "reserved keyword" and perform a specific task. For example, the "var" keyword instructs the browser to create a variable. This article provides a list of the keywords used in JavaScript. It is important to remember that a "variable" or "function" cannot use keywords. This is another interactive reference to use as you learn to write JavaScript statements.
Reserved keywords as of ECMAScript 2015
Please select a keyword to learn about the syntax and run an example.
breakcasecatchclassconstcontinuedebuggerdefaultdeletedoelseexportextendsfinallyforfunctionifimportininstanceofnewreturnsuperswitchthisthrowtrytypeofvarvoidwhilewithyield
Source: Mozilla, https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Lexical_grammar#keywords
This work is licensed under a Creative Commons Attribution-ShareAlike 2.5 License.
Future reserved keywords
The following are reserved as future keywords by the ECMAScript specification. They have no special functionality at present, but they might at some future time, so they cannot be used as identifiers.
These are always reserved:
enum
The following are only reserved when they are found in strict mode code or async function bodies::
implementsinterfaceletpackageprivateprotectedpublicstaticyield
The following are only reserved when they are found in module code:
await
The following are only reserved when they are found in strict mode:
let
Future reserved keywords in older standards
The following are reserved as future keywords by older ECMAScript specifications (ECMAScript 1 till 3).
abstractbooleanbytechardoublefinalfloatgotointlongnativeshortsynchronizedthrowstransientvolatile
Additionally, the literals null, true, and false cannot be used as identifiers in ECMAScript.
Reserved word usage
Reserved words actually only apply to Identifiers (vs. IdentifierNames) . As described in es5.github.com/#A.1, these are all IdentifierNames which do not exclude ReservedWords.
a.import
a['import']
a = { import: 'test' }.
On the other hand the following is illegal because it's an Identifier, which is an IdentifierName without the reserved words. Identifiers are used for FunctionDeclaration, FunctionExpression, VariableDeclaration and so on. IdentifierNames are used for MemberExpression,CallExpression and so on.
function import() {} // Illegal.Identifiers with special meanings
A few identifiers have a special meaning in some contexts without being keywords of any kind. They include:
argumentsgetset