Discuss
  • Class extending function/generator/class literals

Class extending function/generator/class literals

# Isiah Meadows (11 years ago)

I know this wouldn't be a common use case, but might come into play with minifiers later on. Would any of the following be potentially valid in ES6?

class Foo extends function() {} { /* class body */ }
class Foo extends function* (bar) { yield bar } { /* class body */ }
class Foo extends class { /* super body */ } { /* class body */ }

This question came from the fact that classes can be stored in variables like so:

let Foo = class Bar { /* ... */ }
# Rick Waldron (11 years ago)

On Sun, Aug 24, 2014 at 3:22 PM, Isiah Meadows <impinball at gmail.com> wrote:

I know this wouldn't be a common use case, but might come into play with minifiers later on. Would any of the following be potentially valid in ES6?

class Foo extends function() {} { /* class body */ }

This is valid:

  class F extends function () { this.prop = 1; } {
    constructor() {
      super();
    }
  }

  var f = new F();
  console.log(f.prop === 1); //  true

 class Foo extends function* (bar) { yield bar } { /* class body */ }

This won't work correctly: the constructor method of Foo can't be a generator method: people.mozilla.org/~jorendorff/es6-draft.html#sec-static-semantics-constructormethod , people.mozilla.org/~jorendorff/es6-draft.html#sec-runtime-semantics-classdefinitionevaluation. This is all further detailed here: people.mozilla.org/~jorendorff/es6-draft.html#sec-generatorfunction-objects, specifically: people.mozilla.org/~jorendorff/es6-draft.html#sec-generatorfunction-constructor

class Foo extends class { /* super body */ } { /* class body */ }

This is valid:

  class C extends class { get() { return 1; } } {
    constructor() {
      super();
    }
  }

  var c = new C();

  console.log(c.get() === 1); // true