Question

I’ve been using the Youtube json api for making a new mash-up.
Somewhere in the response you can find the following:

{
"player":
  {
  "default":"http://www.youtube.com/watch?v\u003deH5Iysm417U"
  }
}

I’ve always learned not to use any words mentioned in the reserved words section of the ECMAScript standard as identifiers. So as far as I know it’s not allowed to use the name “default” as a property name. Why is Youtube doing this?

player.default

To be honest, the above code works fine in a browser. But I had to change it to the code beneath in order to have no compile errors when using the Google closure compiler.

player["default"]

It just feels wrong.
The most important question here is, can I do anything about it?

Answer 1

An Identifier is not the same as a PropertyName.

PropertyName need only not consist of reserved words when declared without quotes. When declared with quotes, then all strings are valid, even " ".

Here is the list of the valid productions:

 PropertyName :    
     Identifier    
     StringLiteral    
     NumericLiteral

http://www.ecma-international.org/publications/files/ECMA-ST-ARCH/ECMA-262,%203rd%20edition,%20December%201999.pdf, 11.1.15

You cannot change the response from Youtube, and allthough there is nothing wrong with player.default, you will simply need to use the [] accessor if you want to avoid this error in the closure compiler.

But really, this is a bug with the compiler, not the javascript.