Stores recently viewed urls to local storage along with their view times

addToRecentlyViewed.js

/**
 * Stores recently viewed urls to local storage along with their view times
 *
 * @param {String} key - the localStorage key where the list is stored
 * @param {String} url - the location of the page that was viewed
 * @param {Object} json - arbitrary json blob associated with a url
 * @param {Integer} limit - the max number of urls to save
 */
function addToRecentlyViewed (key, url, json, limit) {

  var viewedAt = Date.now(),
    recentlyViewed = localStorage[key],
    alreadyInRecents = false,
    limit = (limit) ? limit : 20;

  // initialize the local storage recent views if it hasn't been

  try {
    recentlyViewed = (recentlyViewed) ? JSON.parse(recentlyViewed) : [];
  } catch(e) {
    console.log('Error parsing json of recently viewed items');
    recentlyViewed = [];
  }

  // if the url is already in the set, update the view time and the data

  for (var i=0; i < recentlyViewed.length && !alreadyInRecents; i++) {
    if (recentlyViewed[i]["url"] && recentlyViewed[i]["url"] === url) {
      recentlyViewed[i]["viewedAt"] = viewedAt;
      recentlyViewed[i]["json"] = json;
      alreadyInRecents = true;
    }
  }

  // add the url to the recently viewed list if it wasn't updated in place

  if (!alreadyInRecents) {
    recentlyViewed.unshift({ url: url, viewedAt: viewedAt, json: json });
  }

  // sort urls by recently viewed times descending

  recentlyViewed.sort( function(a,b) {
    if ( a.viewedAt > b.viewedAt ) return -1;
    if ( a.viewedAt < b.viewedAt ) return 1;
    return 0;
  });

  // save a limited list of recently viewed items to local storage

  localStorage[key] = JSON.stringify( recentlyViewed.slice(0, limit) );
}