Baseline Widely available
The class keyword can be used to define a class inside an expression.
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.
This is just an anonymous class expression which you can refer to using the variable 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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