Typescript multiple inheritance

Question

I'm need of multiple inheritance in typescript. Logically it is not good to put a lot of functionality to hierarchy. I have one base class and number of hierarchy branches. But I need somehow to use mixings to put some main logic in separate classes, cuz it is not used in every branch.

UPDATE of code exmple:

function Mixin = function(mixins:any[]){ // mixin decorator     return function(target){         mixins.forEach((mixin) => {             add every function from mixing to target prototype,              if functions with same name does not exists there,             so we are able to do calls to as example different render() functions                 Will show it in OpenableItem                 });     } }  function element = function(){     return function(target){         target.prototype.element = function(){             return this.$el;         }     } } -------------------------------------------------------------------------------------- @element // every item will have this function as Root as Openable class BaseItem{     y() => number; // we need to get y position of every item } OpenableMixin{     render() => render arrow only     open(){} => change arrow position and cause menu to fire change event     close(){} => change arrow position and cause menu to fire change event } class ItemsMixin extends OpenableMixing{// for now if item have childs it must be openable,                      // but Responsive has only tasks and must be openable too     addItem(item: BaseItem) // need to add generics     removeItem(item: BaseItem)   } -------------------------------------------------------------------------------------- @Mixin([ItemsMixin, ActivitiesMixin]) // it can have items and activities class OpenableItem extends BaseItem implement ItemsMixin, ActivitiesMixin { // as in typescript docs     render(){         // call rendering from BaseItem class         super.render();         // call rendering from OpenableMixing         OpenableMixin.prototype.render.call(this);         // do some separate rendering for OpenableItem only         this.$el.append('line');     }    }  @Mixin([ItemsMixin]) // it can have items class RootItem extends BaseItem implement ItemsMixin{ // and subitems functionality is only for Root class     subitems: Array<BaseItem> // need to add generics to be able to put here different item types } -------------------------------------------------------------------------------------- @element class Menu{     items: Array<Item> }  @element class Timeline{     menu: Menu     listAllelement() => {         console.log(this.element());         console.log(this.menu.element());         this.menu.items.forEach((item) => {             console.log(item.element());             if(item.hasChilds()){  // really it must be (item instanceof RootItem || item instanceof OpenableItem)                 item.items.forEach((subitem) => { // really we need some recursion here                     console.log(subitem.element());                 })             }         })     } } 

In reality it is rare situation when you need to implement multiple inheritance, and it is much rarely when you can have such an issue in javascript. But every item can have different functionality depending on needs.

Just imagine that there can be different items which can have number of mixins. Is it wise to put everything into base ? And what is your approach to this issue ?

Answer 1

TypeScript 2.2 added support for the ECMAscript 2017 mixin pattern

Here is a full code sample:

// http://justinfagnani.com/2015/12/21/real-mixins-with-javascript-classes/ // https://github.com/Microsoft/TypeScript/wiki/What's-new-in-TypeScript#support-for-mix-in-classes  type Constructor<T> = new (...args: any[]) => T;  class S {   foo() {     console.log('foo from S');   } }  // Here the possible SuperClass is set to {} (Object) function Mixin1<T extends Constructor<{}>>(SuperClass: T) {   return class extends SuperClass {     foo() {       console.log('foo from Mixin1');       if (super.foo) super.foo();     }   }; }  // Here the possible SuperClass (S) is specified function Mixin2<T extends Constructor<S>>(SuperClass: T) {   return class extends SuperClass {     foo() {       console.log('foo from Mixin2');       super.foo();     }   }; }  class C extends Mixin1(Mixin2(S)) {   foo() {     console.log('foo from C');     super.foo();   } }  new C().foo(); 

This outputs:

foo from C foo from Mixin1 foo from Mixin2 foo from S