Today in one of my new tenants I got the following errors in my search result web part:

Sorry, something went wrong.

When I opened up the error I got the following details:
Display Error: The display template had an error. You can correct it by fixing the template or by changing the display template used in either the Web Part properties or Result Types.
Template ‘~sitecollection/_catalogs/masterpage/Display Templates/Search/Item_StaffDirectory.js’ not found or has syntax errors. (LoadTemplate: ~sitecollection/_catalogs/masterpage/Display Templates/Search/Group_Default.js)
There was no error anywhere pointing me towards the problem other than the above. I’m sure that in an on-premises version of SharePoint the ULS logs would have been great help. But  I’m on Office 365.
Quite a few errors are given within the SharePoint interface however in this case all I could do is remove sections of my display template and figure out which line caused the problem.
In this case I was using a variable in my has_uEmail

if(has_uEmail  == true) {

_#= uEmail =#_


Somehow one of the code merges had gone slightly wrong and I missed out the following line:

var has_uEmail = !$isEmptyString(ctx.CurrentItem.WorkEmail);

So using a variable that hasn’t been defined is causing SharePoint on Office 365 not to compile the html version of the display template into a JavaScript version of the same.