JavaScript-检查对象中是否存在原型实例

Question

I want to check an object to see if any instances of the carDoor prototype exist

function carDoor(side) {
    this.side = side;
}

var Car = {

    "door1": new carDoor("left"),
    "door2": new carDoor("right")

}

Does the Car object have a door? - How can I check in a way that will work for any prototype?

Assume that you don't know or control the name of the property.

Answer 1

You can use the instanceof operator:

for (key in Car) {
   if (Car.hasOwnProperty(key)) {
      if (Car[key] instanceof carDoor) {
          // ...
      }
   }   
}

Answer 2

In your example, you could do:

Car.door1.constructor === carDoor;

That will return true.

Answer 3

You answered your question.. or at least a half of it, verify the constructor of the Car object properties and it'll return true.

if (Car.door2.constructor === carDoor)
// ...