Register Event Callback is not firing when i add the vunits.js file using javascript

[shmdhussain]

The register event is not firing when I am testing the browser is supporting the viewport units using modernizr and adding the fallback as below

`if(Modernizr && Modernizr.viewportunits){ setTimeout(function(){ addScript('scripts/lib/viewportFallback/vunits.js'); }, 1000)

    alert("not supported vw");
}
else{
  alert("supported vw");
}`

I added the prefixfree.js in the index page initially, i am doing angular application.

The register event is fired when i included it in index page but not fired when i included by javascriopt as above

Thanks in advance for any help.