Like a parasite

parasite.js

Object.prototype.parasiteCopy = function(obj, args)  {
    if(typeof obj.constructor === 'function') {
      obj.apply(this, args);
    }
}

var Plant = function(colour,roots) { 
	this.colour = colour;
	this.roots = roots
}


var Letuce = { hasLeavs: true, height: 13 }

Letuce.parasiteCopy(Plant, ['green',true]);