class expression
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 simple class expression
This is just a simple 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 |
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