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JavaScript

Posted by chazel
chazel
Courses Plus Student 6,961 Points

Passing an Object Function - Uncaught TypeError

Summary

I am trying to pass an object function (either _.convertGold or _.convertSilver in the below example) as an additional function to perform inside a callback function. Normally, inside the swap() method shown below, I could use _.convertGold() or _.convertSilver() to execute those functions.

swap: function () {
  var _ = this;
  var browserWidth = $(window).width();

  function setConversionEvent(state) {
    _.$appEl.trigger($.Event('myModule.App.converted'));
    _.convertedState = state;
  }

  function convert(callback, fn, state) {
    fn();
    callback(state);
  }

  if (browserWidth <= 768) {
    if (_.convertedState === 'silver') {
      convert(setConversionEvent, _.convertGold, 'gold')
    }
  } else {
    if (_.convertedState === 'gold') {
      convert(setConversionEvent, _.convertSilver, 'silver')
    }
  }
},

Problem

When I try passing those functions, I see the following errors:

Firefox: Uncaught TypeError: _ is undefined

Chrome: Uncaught TypeError: Cannot read property '$appEl' of undefined

I am not sure how to resolve "this" problem here. Can anyone help? I have copied below a generic shell of the module pattern I use so you can see the bigger picture of the code structure:

(function ($) {
  'use strict';

  jQuery.fn.extend({
    myModule: function () {

      var App = function (element, options) {
        this.element = element;
        this.options = options;
        this.metadata = $(element).data('app-options');
      };

      App.prototype = {
        events: {
          init: 'myModule.App.init'
        },

        setOptions: function () {
          var _ = this;

          // merge defaults and other options
          _.options = $.extend({}, _.defaults, _.options, _.metadata);
          _.options.error = '';

          // cache element for best performance
          _.$appEl = $(_.element);
        },

        convertSilver: function () {
          var _ = this;
          var el = _.$appEl;

          ...

          _.convertedState = 'silver';
        },

        convertGold: function () {
          var _ = this;
          var el = _.$appEl;

          ...

          _.convertedState = 'gold';
        },

        swap: function () {
          var _ = this;
          var browserWidth = $(window).width();

          function setConversionEvent(state) {
            _.$appEl.trigger($.Event('myModule.App.converted'));
            _.convertedState = state;
          }

          function convert(callback, fn, state) {
            fn();
            callback(state);
          }

          if (browserWidth <= 768) {
            if (_.convertedState === 'silver') {
              convert(setConversionEvent, _.convertGold, 'gold')
            }
          } else {
            if (_.convertedState === 'gold') {
              convert(setConversionEvent, _.convertSilver, 'silver')
            }
          }
        },

        watchBrowser: function () {
          var _ = this;

          $(window).on('load resize', function () {
            _.swap();
          });
        },

        setActions: function () {
          var _ = this;

          ...

        },

        init: function () {
          var _ = this;

          _.setOptions();
          _.$appEl.trigger($.Event(_.events.init));

          _.convertedState = 'silver'; // set initial state before conversion

          _.swap();
          _.watchBrowser();
          _.setActions();
        }
      };

      App.defaults = App.prototype.defaults;

      $.fn.app = function (options) {
        return this.each(function (i, element) {
          new App(element, options).init();
        });
      };

      window.App = App;

      $(window).on('load', function () {
        $('[data-app-options]').app();
      });
    }
  });
  jQuery(document).myModule();