main.js

chrome.browserAction.onClicked.addListener(function(tab) {
  chrome.storage.sync.get(null, function(data) {
    var queryParam = '';
    var keys = Object.keys(data);
    if (keys.length > 0) {
      for (var i = 0; i < keys.length; i++)
      {
        if(keys[i].includes("reactant"))
        {
          var reactantKey = keys[i];
          var index = parseInt(reactantKey.substring(reactantKey.length - 1, reactantKey.length));
          if(data['active'] == parseInt(index)) {
            var productKey = "product_" + index;
            queryParam = data[reactantKey] + '=' + data[productKey]
          }
        }
      }
    } else {
      queryParam = 'xYextDebug=true';
    }

    chrome.tabs.query({'active': true, 'lastFocusedWindow': true}, function (tabs) {
      var url = tabs[0].url;
      var queryParams = [];
      if(url.indexOf("?") > -1) {
        queryParams = url.substring(url.indexOf("?"), url.length).replace("?", "").split("&");
      }

      if(!queryParams.includes(queryParam)) {
        queryParams.push(queryParam);
      } else {
        var paramIndex = queryParams.indexOf(queryParam);
        queryParams.splice(paramIndex, 1);
      }

      newUrl = "";
      if(url.indexOf("?") > -1) {
        newUrl = url.substring(0, url.indexOf("?"));
      } else {
        newUrl = url;
      }

      for(var i = 0; i < queryParams.length; i++) {
        if (i == 0) {
          newUrl = newUrl + "?" + queryParams[i];
        } else {
          newUrl = newUrl + "&" + queryParams[i];
        }
      }

      chrome.tabs.update({
       url: newUrl
      });
    });
  });
});