Best Way to Add Methods to Existing Javascript Object

Question

I am receiving an ajax feed of documents that looks something like this (much simplified):

aDocs = [{title:'new doc', ext:'pdf'}, {title:'another', ext:'xlsx'}];

I am going to iterate through the aDocs array and display information about each doc, while adding some methods to each doc that will allow for modifying the HTML for display and making API calls to update the database.

I read here that in order to add methods to existing objects, you can use the __proto__ attribute. Something along the lines of:

function Doc(){}
Doc.prototype.getExt = function(){return this.ext}
Doc.prototype.getTitle = function(){return this.title}
for (var i=0; i<aDocs.length; i++){
  aDocs[i].__proto__ = Doc.prototype
}

According to that article above,this isn't official javascript, isn't supported by IE (never will be), and will likely be deprecated in webkit browsers.

Here's an alternative stab at it:

function getExt(){ return this.ext }
function getTitle(){return this.title}
for (var i=0; i<aDocs.length; i++){
  aDocs[i].getExt = getExt;
  aDocs[i].getTitle = getTitle;
}

Is this second alternative viable and efficient? Or am I re-creating those functions and thereby creating redundant overhead?

Again the above examples are simplified (I know aDocs[i].ext will solve the problem above, but my methods for display and API calls are more complicated).

Answer 1

Is this second alternative viable and efficient?

Yes.

Or am I re-creating those functions and thereby creating redundant overhead?

No, the functions are reused, not re-created. All of the objects will share the single copy of the getExt and getTitle functions. During the call to the functions from (say) aDocs[1], within the call, this will refer to the object the function is attached to. (This only applies if you call it as part of an expression retrieving it from the object, e.g., var title = aDocs[1].getTitle();)

Alternately, if you liked, you could create new objects which shared a prototype, and copy the properties from the aDocs objects to the new objects, but you've asked about assigning new functions to existing objects, so...