模板助手中使用Meteor中的全局助手的例外情况

Question

I added a global helper function with UI.registerHelper which returns a String. If I access the particular site, I can see the correct output , but I get the following exception:

Exception in template helper: http://localhost:3000/client/helpers/global_helpers.js?c1af37eca945292843a79e68a3037c17a0cfc841:18:45
http://localhost:3000/packages/blaze.js?cf9aea283fb9b9d61971a3b466bff429f9d66d7d:2458:21

This is my code:

UI.registerHelper('levelMode', function() {
    return Games.findOne({_id: this._id}).mode ? 'Difficult' : 'Easy';
});

Any ideas how to solve this issue?

Answer 1

Try adding some checks:

UI.registerHelper('levelMode', function() {
  if (typeof Games !== 'undefined' && Games != null)
    var game = Games.findOne({_id: this._id});
    if (game != null && game.mode)
      return 'Difficult';
  return 'Easy';
});

My hunch is that the error stems from the cases where Games isn't yet defined (the template is rendering before the collection is defined) or findOne returns null (nothing found). You can't access a mode property of null .