Dynamics CRM 2016 and Use Legacy form rendering

So you may know that Microsoft has improved form load by doing some extensive caching.  There is a setting under General Settings called "Use Legacy form rendering" which you can set to Yes or No.

Now you might wonder why I am writing a post about this setting. Well it was a JavaScript  error on a Form Load that I was getting. I had my own JavaScript code on the Form Load  but the error shown was confusing:
Field:window
Event:onload
Error:Unable to get property '$o_3' of undefined or null reference

Huh? A bit of Googling showed that others had come across it to

https://patricda.wordpress.com/2015/09/18/jscript-unable-to-get-property-o_3-of-undefined-or-null-reference-crm-2015-update1-0/

The post included this comment "Note that this error only occurs when you turn on the “Use Legacy form rendering”.  Sure enough changing this setting to No avoids the error. 

But what if you want to preserve the faster form rendering?  Patric provide the solution in his blog. 
Add the following line before calling the prefilter function.

Xrm.Page.getControl(“EntityName”)._control && Xrm.Page.getControl(“EntityName”)._control.tryCompleteOnDemandInitialization && Xrm.Page.getControl(“EntityName”)._control.tryCompleteOnDemandInitialization();

Brilliant.