Lightning Components can benefit from the Chrome console to a greater extent for JavaScript debugging. You can use console.log() to debug the variable value.

Observe how, in the following code snippet, we console.log the request parameters and also the response values from the backend Apex method:

setSearchTerm : function(component, event) {
          var searchTerm = component.find('searchBox').getElement().value;
console.log(searchTerm);
           component.set("v.searchTerm",searchTerm);
           // create a one-time use instance of the search action
          // in the server-side controller

          var action = component.get("c.search");
          action.setStorable();
          action.setParams({ searchstr : searchTerm});
          action.setCallback(this, function(response) {
              var state = response.getState();
              if (state === "SUCCESS") {
                  var responseData = JSON.parse(response.getReturnValue());
     ...