Make Backbone Collections and Models aware of their current sync state

backbone-inflight.js

// Patch Backbone Model and Collection to have awareness
//  of current sync state.
// Adds an isLoading method and _inFlight count property.
// Fires before:sync and after:sync events.
// Based on http://tbranyen.com/post/how-to-indicate-backbone-fetch-progress
!function() {
  function onSyncEnd() {
    -- this._inFlight;
    this.trigger("after:sync", this);
  }

  _.each([Backbone.Model, Backbone.Collection], function(Type) {
    var originalSync = Type.prototype.sync;

    Type.prototype._inFlight = 0;
    Type.prototype.isLoading = function() {
      return this._inFlight > 0;
    }

    Type.prototype.sync = function() {
      var synced = onSyncEnd.bind(this);

      this.trigger("before:sync", this);
      ++ this._inFlight;

      return originalSync.apply(this, arguments)
        .then(synced, synced);
    };
  });
}();