js/libs/ember-data.js
function(type, id) {
    id = coerceId(id);
    type = this.modelFor(type);
    return !!this.typeMapFor(type).idToRecord[id];
  }
function(type, id) {
    id = coerceId(id);
    type = this.modelFor(type);
    return !!this.typeMapFor(type).idToRecord[id];
  }
Returns true if a record for a given type and ID is already loaded.

@method hasRecordForId
@param {String or subclass of DS.Model} type
@param {String|Integer} id
@returns {Boolean}