meteor__microscope/client/templates/posts/post_submit.js

Template.postSubmit.onCreated(function () {
  Session.set('postSubmitErrors', {});
});

Template.postSubmit.helpers({
  errorMessage: function (field) {
    return Session.get('postSubmitErrors')[field];
  },

  errorClass: function (field) {
    return !!Session.get('postSubmitErrors')[field] ? 'has-error' : '';
  }
});

Template.postSubmit.events({
  'submit form': function (e) {
    e.preventDefault();

    var post = {
      url: $(e.target).find('[name=url]').val(),
      title: $(e.target).find('[name=title]').val()
    };

    var errors = validatePost(post);
    if (errors.title || errors.url) {
      Session.set('postSubmitErrors', errors);
      // We return to abort the helper, not for anyone using the result.
      return;
    }

    Meteor.call('postInsert', post, function (error, result) {
      // Display the error to the user and abort.
      if (error) {
        return throwError(error.reason);
      }

      // Show this result but route anyway.
      if (result.postExists) {
        throwError("This link has already been posted");
      }

      Router.go('postPage', { _id: result._id });
    });
  }
});