☁ Ajit-On-Cloud ☁ : What makes Visualforce In Salesforce Classic & Lightning Experience different?

1) Development Mode for Visualforce is only available in Salesforce Classic and not in Lightning.

2) Pages you view using direct URL access always display in Salesforce Classic and not in Lightning. The reason is in order to view your page in Lightning Experience, you need to access the Lightning Experience container app. This means accessing /one/one.app. If you’re accessing that, you can’t access /apex/PageName. They’re just two different URLs that don’t overlap.

To test your page in Lightning Experience, add the following bookmarklet to your browser’s menu or toolbar -

javascript:(function(){
var pageName = prompt('Visualforce page name:');
$A.get("e.force:navigateToURL").setParams(
{"url": "/apex/" + pageName}).fire();})();

3) Use the $User.UITheme and $User.UIThemeDisplayed global variables to determine the current user experience context in Visualforce context. These global variables return a string that uniquely identifies the current user interface context. The difference between the two variables is that $User.UITheme returns the look and feel the user is supposed to see, while $User.UIThemeDisplayed returns the look and feel the user actually sees.

The possible values for $User.UITheme and $User.UIThemeDisplayed are the same:

Theme1—Obsolete Salesforce theme
Theme2—Salesforce Classic 2005 user interface theme
Theme3—Salesforce Classic 2010 user interface theme
Theme4d—Modern “Lightning Experience” Salesforce theme
Theme4t—Salesforce1 mobile Salesforce theme
PortalDefault—Salesforce Customer Portal theme
Webstore—Salesforce AppExchange theme

4) Use the UserInfo.getUiTheme() and UserInfo.getUiThemeDisplayed() system methods to determine the current user experience context in Apex code. The possible values returned by these methods are the same as those returned by the $User.UITheme and $User.UIThemeDisplayed global variables.

5) Lightning Experience manages navigation using "Events" (use 'sforce.one' object) while in Salesforce Classic we have "PageReference" for performing navigation actions.

6) Use <apex:slds> component to reference Lightning Design System stylesheets without uploading them as a static resource, simplifying the syntax of your page and preventing you from hitting the 250-mb static resource limit.

7) Some more differences that we can make in between Visualforce page running in Salesforce Classic compared to Lightning Experience are -

a) In Salesforce Classic, Visualforce “owns” the page. But in Lightning Experience, Visualforce runs inside an iframe that’s wrapped inside the larger Lightning Experience container.
b) Lightning Experience and Visualforce pages are not only held in different browser contexts, they’re also served from different domains. So, even though it’s all showing in one browser window, the session ID inside the Visualforce iframe will be different than the session ID outside the iframe, in another part of Lightning Experience.
c) <apex:page> showHeader and sidebar attributes are always false.