Is it possible to create some property in JavaScript that contain some methods?

Question

Please look at my required JavaScript.

var someVariable = new SomeDataType();

// I can directly access value of its property.
someVariable.someProperty = "test";
alert(someVariable.someProperty); // <- this command must should "test"

// However, I have some methods in above property

// I want to validate all rule in this property.
someVariable.someProperty.isValid(); // <- this method will return true/false

Is it possible for doing this in current version of JavaScript?

UPDATE

Please look as my answer!

Answer 1

someVariable.someProperty = [ test, anotherFunc, yetAnotherFunc];
someVariable.somePropertyAllValid= function() {
   for(var prop in someVariable.someProperty) {
      if(!prop()) return false;
   }
   return true;
};

someVariable.somePropertyAllValid();

Answer 2

Yes, you can assign Javascript functions as properties like this:

someVariable.someProperty = function (arg1, arg2) {
  // function code goes here
};

This is the method using function literals.

Another method is to use function instances like this:

someVariable.someProperty = new Function (arg1, arg2, code);

Note that in the second method, the code goes in as the last parameter and the Function keyword has a capitalized 'F' as against method 1 where the 'f' is small.

Further, creating a function instance inside a loop etc. will create an entire new instance to assign which is inefficient in memory. This problem does not arise while using the function literal method.

Answer 3

You can't (and probably shouldn't) treat objects like that in JavaScript. As someone else mentioned, you can override the toString() method to get half of the functionality (the read portion), but you cannot use the assignment operator on an object like that without overwriting the object.

You should choose a different approach, like using nested objects (as CMS suggested).

Answer 4

I just found the answer. It's very simple & clean.

function createProperty(value, defaultValue, ruleCollection)
{
    this.value = value;
    this.defaultValue = defaultValue;
    this.ruleCollection = ruleCollection;       
}

createProperty.prototype.toString = function()
{
    return this.value;
};

var someVariable = 
{
    someProperty: new createProperty
    (
        'currentValue',
        'defaultValue',
        null
    )
};

For testing, you can use something like my following code.

var test = ">>" + someVariable.someProperty + "<<";

// this alert must shows ">> currentValue <<"
alert(test);


someVariable = 
{
    someProperty: new createProperty
    (
        7,
        5,
        null
    )
};

test = someVariable.someProperty + 3;

// This alert must shows "10"
alert(test);

I just test it on FF 3.5 & IE 8. It works fine!

Update

Oops! I forget it. Because this technique returns object reference for this property. So, it's impossible to directly set property data. It isn't my final answer.

Answer 5

Its possible, but with the below change in your code

function SomeDataType(){
 var localProperty="";
 this.someProperty = function(txt){
  if (arguments.length==0)
   return localProperty;
  else
   localProperty=txt;
 }  
 this.someProperty.isValid = function(){
   return (localProperty!="") ? true : false;

 };
}

instead of defining someProperty as a property, define this as function which sets value to the local property if any value is passed or it ll return that property value if no argument is given.

var someVariable = new SomeDataType();
someVariable.someProperty("test");
alert(someVariable.someProperty()); 

var isValid = someVariable.someProperty.isValid();

this is how you need to access the SomeDataType object.

Cheers

Ramesh Vel

Answer 6

Perhaps this would be of help:

var SomeVar = {
  someProperty : {
    value : 7,
    add : function (val) {
      this.value += parseInt(val, 10);
      return this;
    },
    toString : function () {
      return this.value;
    }
  }
}

alert(SomeVar.someProperty.add(3));