I need to make it so that every time a specific property on my object is changed - it will call a special method on the same object.

Example:

MyObject.prototype = Object.create({
    specialMethod: function() { /* ... */ }
  }, {
    someValue: {
      set: function(value) {

        /* HOW DO I ASSIGN THE VALUE TO MyObject HERE?*/
        /* I can't do: this.someValue=value, that would create endless recursion */

        this.specialMethod();
      }
    }
  });

How do I assign the value to MyObject within the property setter?

I need to make it so that every time a specific property on my object is changed - it will call a special method on the same object.

Example:

MyObject.prototype = Object.create({
    specialMethod: function() { /* ... */ }
  }, {
    someValue: {
      set: function(value) {

        /* HOW DO I ASSIGN THE VALUE TO MyObject HERE?*/
        /* I can't do: this.someValue=value, that would create endless recursion */

        this.specialMethod();
      }
    }
  });

How do I assign the value to MyObject within the property setter?

• javascript
• oop
• setter
• defineproperty

• Assigning MyObject would ruin all that. You could theoretically do MyObject = value, but as i said, that destroys the prototype. – Scimonster Commented Sep 23, 2014 at 14:58
• Why would you want to overwrite MyObject? – Bergi Commented Sep 23, 2014 at 14:58
• 2 I assume you simply want to assign a property of the current MyObject instance? Just use this as always. – Bergi Commented Sep 23, 2014 at 14:59
• @Bergi, I can't that would create an endless recursion, cause assigning this.someValue calls the setter – YemSalat Commented Sep 23, 2014 at 15:00
• 1 @YemSalat: You didn't tell us which property you wanted to assign to. this.MyValue = value would work flawlessly… – Bergi Commented Sep 23, 2014 at 15:03

1 Answer 1

There is no storage place in a getter/setter property, you cannot store values on it. You need to store it somewhere else and create a getter for that. Two solutions:

1. Use a second, "hidden" property:

   MyObject.prototype.specialMethod: function() { /* ... */ };
   Object.defineProperty(MyObject.prototype, "someValue", {
       set: function(value) {
           this._someValue = value;
           this.specialMethod();
       },
       get: function() {
           return this._someValue;
       }
   });
   

2. Use a closure variable (typically created on construction of the instance):

   function MyObject() {
       var value;
       Object.defineProperty(this, "someValue", {
           set: function(v) {
               value = v;
               this.specialMethod();
           },
           get: function() {
               return value;
           }
       });
   }
   MyObject.prototype.specialMethod: function() { /* ... */ };