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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.
class
You can also define classes using the class declaration.
const Rectangle = class { constructor(height, width) { this.height = height; this.width = width; } area() { return this.height * this.width; } }; console.log(new Rectangle(5, 8).area()); // Expected output: 40
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.
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.
SyntaxError
This is just an anonymous class expression which you can refer to using the variable Foo.
Foo
const Foo = class { constructor() {} bar() { return "Hello World!"; } }; const instance = new Foo(); instance.bar(); // "Hello World!" Foo.name; // "Foo"
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.
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"
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