Adds client-side logging of collection activity and template rendered events. Toggled via localStorage.

trace.js

//////////////////////////////////////////////////////////////////////
// Use localStorage to toggle logging of collection activity and
// template rendering
//
// Put this file in 'client/lib/trace.js'
//
// Toggle via browser console:
//   localStorage.setItem('Meteor.traceCollections', true)
//   localStorage.setItem('Meteor.traceRendered', true)
//
//////////////////////////////////////////////////////////////////////

"use strict";

Meteor.traceCollections = false;
Meteor.traceRendered = false;


//////////////////////////////////////////////////////////////////////
// Check localStorage flags to see what we should log to console
//

if (supports_html5_storage()) {
  Meteor.traceCollections = !!window.localStorage.getItem('Meteor.traceCollections');
  Meteor.traceRendered = !!window.localStorage.getItem('Meteor.traceRendered');
}


/**
 * Tests whether localstorage is supported in the user's client
 * source: http://diveintohtml5.info/storage.html
 *
 * @method supports_html5_storage
 * @returns {Boolean} true if localstorage is supported
 */
function supports_html5_storage () {
  try {
    return 'localStorage' in window && window['localStorage'] !== null;
  } catch (e) {
    return false;
  }
}


//////////////////////////////////////////////////////////////////////
// traceCollections
//

if (Meteor.traceCollections) {
  var Collection,
      originalFn;

  console.log('[trace] wrapping Collection.find');

  Collection = 'undefined' === typeof Mongo ? Meteor.Collection
                                            : Mongo.Collection;
  originalFn = Collection.prototype.find;

  Collection.prototype.find = function () {
    var cursor = originalFn.apply(this, arguments),
        collectionName = this._name;
   
    cursor.observeChanges({
      added: function (id, fields) {
        console.log('[trace]', collectionName, 'added', id, fields);
      },
   
      changed: function (id, fields) {
        console.log('[trace]', collectionName, 'changed', id, fields);
      },
   
      movedBefore: function (id, before) {
        console.log('[trace]', collectionName, 'movedBefore', id, before);
      },
   
      removed: function (id) {
        console.log('[trace]', collectionName, 'removed', id);
      }
    });
   
    return cursor;
  };
}




//////////////////////////////////////////////////////////////////////
// traceRendered
//

if (Meteor.traceRendered) {
  Meteor.startup(function () {
    var name,
        template;

    console.log('[trace] wrapping Template.rendered');

    for (name in Template) {
      template = Template[name];
      if (template && template.rendered) {
        wrapRendered(template, name);
      }
    }
  })
}

function wrapRendered(template, name) {
  Template[name].rendered = _.wrap(template.rendered, function (func) {
    var args = Array.prototype.splice.call(arguments, 0, 1);

    console.log('[trace] rendered', name);
    func.apply(this, args);
  })
}