Question

I have several aspx pages and one site.master. I defined *.js file with any javascript functions.
And now I want to find ID of FileUpload control on one of this subpage.

function CheckFile()
{

var filePath = document.getElementById('<%= this.fileUp.ClientID %>').value;

but it doesn’t work.

Answer 1

You can only use server-side code in ASPX pages, not standalone .js files

Instead, you should pass the control’s ID from inline Javascript in your ASPX.