CODEWITHSUNDEEP
javascriptjqueryobjectproperties
JimiiBee
JimiiBee

Reputation: 159

Setting property value from other property value inside object

Is there a way to set the value of a property within an object relative to another property within the same object?

For example:

var myObj = {
    prop1 = 10,
    prop2 = prop1 + 5
};

alert(myObj.prop2); //Alerts 15

Another example would be for when I create objects within an object aswell

var mainObj = {
    obj1: {x: 100, y:100},
    obj2: {x: obj1+10, y: obj1+10}
};

alert(mainObj.obj2.x); //Alerts 110

I want certain properties to stay relative to other properties in the same object, so that when I change one property, it will affect the other property.

Upvotes: 6

Views: 6120

Answers (3)

Apostolos Grammatopoulos
Apostolos Grammatopoulos

Reputation: 33

The marked answer is a way around using a function instead of a property. The correct answer to the initial question is using the get syntax.

The difference is shown in the following example:

var myObj = {
    prop1 = 10,
    get prop2(){this.prop1 + 5}
    prop3 : function(){return this.prop1 + 5}
};

console.log(myObj.prop2); // Prints: 15
console.log(myObj.prop3()); // Prints: 15

Similar post/answer.

Upvotes: 3

Witiko
Witiko

Reputation: 3387

If you don't care about backwards compatibility with browsers that only support ECMAScript 3, you can use accessors (setters and getters) featured in ECMAScript 5:

var myObj = Object.create(null, {
  prop1: {
    writable: true,
    configurable: true,
    value: 10
  }, prop2: {
    get: function() {
      return this.prop1 + 5;
    }
  }
});

myObj.prop1       // 10
myObj.prop2       // 15
myObj.prop1 = 20  // 20
myObj.prop2       // 25
myObj.prop2 = 6   // 6
myObj.prop2       // 25

See also the Object.defineProperty() method, which allows you to add accessors to already existing objects.

Upvotes: 0

Chop
Chop

Reputation: 534

You can declare your properties as functions

var obj = {
  prop1:1,
  prop2:function(){
    return this.prop1 + 1;
  }
}

Upvotes: 8

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