Typical mixin in js

mixin.js

Object.prototype.mixin = function(obj)  {
    	if(typeof obj === 'object') {
          for(let i in obj) {
              String(i) in this ? `${i} - property exist` : this[i] = obj[i];	
          }	
      }
}

var Vehicle = { works: true, tank: 100, hasWheels: true }

var Car = { works: false, tuning: true }

Car.mixin(Vehicle)