0.6.7 • Public • Published

Mixin-Pro, for javascript multi-inheritance

Mixin is an easy way to repeatedly mix functionality into a prototypical JavaScript class. It automatically takes care of the combination of overriding prototype methods and invoking constructors. Moreover, it will notify a mixed in constructor that is has been mixed into another class. This can be used to construct dependent mixin hierarchies.


Using npm:

    npm install mixin-pro


var Class = require("mixin-pro").createClass;
// use case 1: create a base class
var Bar1 = Class({
  constructor: function Bar1() {},
  t1: function() { console.log('Bar1->t1()'); },
// use case 2: create a class and inherit from a base class
var Bar2 = Class(Bar1, {
  constructor: function Bar2() {},
  t2: function() { console.log('Bar2->t2()'); },
// use case 3: create a class and inherit from multi base classes
var Bar3 = Class([Bar1, Bar2], {
  constructor: function Bar3() {},
  t3: function() { console.log('Bar3->t3()'); },
  t1: function() {
    // call same name method in super class, with apply() or call()
    this.Super('t1').apply(this, arguments);
    // this.Super('t1').call(this, 1, 2, 3);
// check an object is instance of the inherited base class
var bar3 = new Bar3();
console.log(bar3.instanceOf(Bar3)); // true
console.log(bar3.instanceOf(Bar1)); // true
console.log(bar3.instanceOf(Bar2)); // true
bar3.t1(); // Bar1->t1()   Bar3->t1()
bar3.t2(); // Bar2->t2()
bar3.t3(); // Bar3->t3()

Of course, the mixin-pro can also be used in traditional style:

    var mixin = require("mixin-pro");
    // traditional: create base class Foo, Foo1, Foo2, ...
    function Foo() {}
    Foo.prototype = {
       t0: function() { console.log('Foo->t0()'); }
    // normal mixin: add features to existing classes
    Foo1 = mixin(Foo1, Foo2);



  • mixin.createClass(definition)
  • mixin.createClass(base, definition)
  • mixin.createClass([base1, base2, ...], definition)
var definition = {
  constructor: function Bar3() {},
  t3: function() { return 't3'; },

constructor is required, and the function Bar3 must be named, it will be used as your new class name.

When a new class object constructed, the constructors of the inherited base classes will be called in order.


Check whether obj is an instance of BaseClass or derived class.


Get method with given name defined in base class, will return a function object, which can be called with call(obj, arg1, arg2, ...) or apply(obj, arguments).

Will throw error if the method is not defined in base class.

mixin(base, mixed)

The call mixin(base, mixed) returns a new constructor that adds the prototype for mixed at the back of the prototype chain for base and invokes the constructors for both base and mixed in reverse order. If mixed has function property included, then this function will be invoked with this = mixed and the new constructor class as the single argument.

A constructor to be mixed in cannot have a prototype chain of its own (i.e. it can't itself be the product of a mixin), however this functionality can be achieved by calling mixin again inside the included callback. Moreover, the same constructor can not be mixed in twice to the same prototypical inheritance chain.


If ctor is mixed in to another constructor (e.g. by invoking mixin(Base, ctor)) then ctor.included(base) is called with the this set to the mixed in constructor (e.g. ctor) and is passed a single argument, the new constructor created by mixin(). This is extremely useful for creating dependent chains of mixins (i.e. Mixin1 requires Mixin2) since mixin itself can be invoked from within the included call.

If included returns a value, then it is used as the constructor for the call to mixin that invoked this function. This behavior leads to the useful idiom:

    Foo.included = function(ctor) {
        return mixin(ctor, EventEmitter);

to mix the functionality of EventEmitter into any constructor that mixes in Foo.

mixin.alias(obj, name, suffix, fun)

Can be used to override a method already defined on obj. It assigns fun to obj[name+'_with_"+suffix] and reassigns the current value of obj[name] to obj[name+'_without_'+suffix]. Finally it sets obj[name] to fun. This is similar to Rails' 'alias_method_chain`.

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npm i mixin-pro

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