Question

A clientside javascript library I’ve developed uses objects as hashes in some areas. It loops through objects parsed from Json data with a for…in loop using the property name as a key. eg… (pseudo code)

var conversations = {'sha1-string':{name:'foo',messages:[]}}
for(var id in conversations){
    console.log(id);
    console.log(conversations[id].name);
}

Unfortunately MooTools (and Prototype, etc) add methods to the global namespaces, so my for…in loops now iterate through MooTools’ additions (eg. limit, round, times, each), causing errors when it applies logic to them as if it were the data expected.

As it’s a library, I have to expect that it will be used with MooTools, Prototype, etc. Is there an easy way around this problem? My current solution is just to pass the object to a method which strips out the MooTools specific entries and returns the clean object, but this means also checking what Prototype and all similar libraries out there add, and seems to be a backwards way of doing things.

My other solution is to stop relying on the property name as a key, and perform validation in the loops to ensure I’m looking at the data I want to. Before I do that rewriting though, I’m wondering if anyone has a better/existing solution?

Thanks 🙂

Answer 1

If your clientside objects are not inherited from other custom objects, you see if you could use the javascript’s Object.hasOwnProperty method to find out if a certain property exists in the object itself and not up in the inheritance chain via the prototype object.

For browsers that don’t support this method, you can write a wrapper around to check:

  var hasOwnProperty = function(object, property)   {
     if(object.hasOwnProperty)  {
        return object.hasOwnProperty(property);
     }
     var prop = object[property];
     return typeof(prop) !== "undefined" && prop !== 
             object.constructor.prototype[property];
  }

How to use it:

for(var key in someObj) {
  if(hasOwnProperty(someObj, key)) {
    // we are good to go!
  }
}