JSON-RPC - how can one make a unique ID?

Question

When calling a JSON-RPC service what is the most common way to generate a unique ID from a JavaScript client?

REVISED QUESTION:

Typically, a JavaScript JSON-RPC client implements a counting id parameter (e.g. If the last request was id=1, and it hasn't received a response back, the next request is id=2. If the request with id=1 has responded, the next request can be id=1 again). I'm interested in understanding how people typically implement this.

Answer 1

You don't describe the universe in which this needs to be unique.

If you mean absolutely unique, then you're talking about a UUID.

If you need something unique to the endpoint to prevent client-side caching, then this will suffice

var unique = new Date().getTime();

If you need something other than these two then you'll need to be more specific.

EDIT

Maybe something that looks a bit like this

jsonRpcClient = function()
{
  var requestStack = [null];

  this.makeRequest = function()
  {
    var id = this.getAvailableSlot();
    requestStack[id] = new this.request( id, arguments );
  }

  this.getAvailableSlot: function ()
  {
    for ( var i = 0; i < requestStack.length: i++ )
    {
      if ( null == this.requestStack[i] )
      {
        return i;
      }
    }
    return i;
  }

  this.request: function( id, args )
  {
    // request stuff here
    // pass id and whatever else to jsonRpcClient.handleResponse()
  }

  this.handleResponse: function( id )
  {
    var request = requestStack[id];
    requestStack[id] = null;

    // Do whatever with request
  }
};