Comparing With Branch
In addition to the common file versions comparison options, the Subversion integration with WebStorm provides a special command that enables you to compare a file from your local working copy with its version in the selected branch.
To compare a file with its version in a specified branch, do the following:
Select the desired file in the Project Tool Window, or open it in the editor.
From the main VCS menu, or on the context menu of the selection, choose Subversion | Compare with Branch.
In the Compare with Branch popup, select the desired branch. The Compare with Branch dialog in the form of the Differences viewer for files appears.