Traits decorator

traits-decorator.ts

declare const _: _.LoDashStatic

export function traits(...traitsList) {
  return function decorator(constructor: any) {
    const mergedTraits =  _.extend.apply(_, traitsList)
    const {prototype} = constructor
    const {__proto__} = constructor.prototype
    const prototypeClone =  _.clone(prototype) // We use a clone to avoid getting properties on the proto chain
    constructor.prototype = _.extend(prototype, mergedTraits, prototypeClone)
    constructor.prototype.constructor = constructor
    constructor.prototype.__proto__ = __proto__
    constructor.prototype._traits = mergedTraits
  }
}


// Usage
/*
import {movable, killable} from 'game-traits'

@traits(movable, killable)
class Player {
  // We can override traits inherited methods (kill comes from killable) and call the original method via this._traits
  kill(): void{
    console.log('Player is about to die')
    this._traits.kill.call(this) // Unless you know for sure that the traitFn does not have side effects use with .call or .apply
  }
}
*/