# Mixins

# Example of Mixins

To create mixins, simply declare lightweight classes that can be used as "behaviours".

class Flies {
    fly() {
        alert('Is it a bird? Is it a plane?');

class Climbs {
    climb() {
        alert('My spider-sense is tingling.');

class Bulletproof {
    deflect() {
        alert('My wings are a shield of steel.');

You can then apply these behaviours to a composition class:

class BeetleGuy implements Climbs, Bulletproof {
        climb: () => void;
        deflect: () => void;
applyMixins (BeetleGuy, [Climbs, Bulletproof]);

The applyMixins function is needed to do the work of composition.

function applyMixins(derivedCtor: any, baseCtors: any[]) {
    baseCtors.forEach(baseCtor => {
        Object.getOwnPropertyNames(baseCtor.prototype).forEach(name => {
             if (name !== 'constructor') {
                derivedCtor.prototype[name] = baseCtor.prototype[name];

# Syntax

  • class BeetleGuy implements Climbs, Bulletproof { }
  • applyMixins (BeetleGuy, [Climbs, Bulletproof]);

# Parameters

Parameter Description
derivedCtor The class that you want to use as the composition class
baseCtors An array of classes to be added to the composition class

# Remarks

There are three rules to bear in mind with mixins:

  • You use the implements keyword, not the extends keyword when you write your composition class
  • You need to have a matching signature to keep the compiler quiet (but it doesn’t need any real implementation – it will get that from the mixin).
  • You need to call applyMixins with the correct arguments.