class expression

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since March 2016.

The class keyword can be used to define a class inside an expression.

You can also define classes using the class declaration.

Try it

Syntax

js
class {
  // class body
}
class name {
  // class body
}

Note: An expression statement cannot begin with the keyword class to avoid ambiguity with a class declaration. The class keyword only begins an expression when it appears in a context that cannot accept statements.

Description

A class expression is very similar to, and has almost the same syntax as, a class declaration. As with class declarations, the body of a class expression is executed in strict mode. The main difference between a class expression and a class declaration is the class name, which can be omitted in class expressions to create anonymous classes. Class expressions allow you to redefine classes, while redeclaring a class using class declarations throws a SyntaxError. See also the chapter about classes for more information.

Examples

A basic class expression

This is just an anonymous class expression which you can refer to using the variable Foo.

js
const Foo = class {
  constructor() {}
  bar() {
    return "Hello World!";
  }
};

const instance = new Foo();
instance.bar(); // "Hello World!"
Foo.name; // "Foo"

Named class expressions

If you want to refer to the current class inside the class body, you can create a named class expression. The name is only visible within the scope of the class expression itself.

js
const Foo = class NamedFoo {
  constructor() {}
  whoIsThere() {
    return NamedFoo.name;
  }
};
const bar = new Foo();
bar.whoIsThere(); // "NamedFoo"
NamedFoo.name; // ReferenceError: NamedFoo is not defined
Foo.name; // "NamedFoo"

Specifications

Specification
ECMAScript Language Specification
# sec-class-definitions

Browser compatibility

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See also