Web Forms :: Client ID Of A Dynamically Generated Control?

I've recently added a Master Page to my site,but realized that it's caused some problems in my existing JavaScript setup.I am able to use the following code in most places without any issue to get the ClientID: '<%=myControl.ClientID%>'

The problem I have encountere is that I have several pages that add controls dynamically,and then execute events based on an ID that's passed in,where I can't use this line,because I won't know the ID of the control I'm trying to access until the Javascript executes.Here's a simplified version of the problem:

When the page runs,it creates n textboxes dynamically,and appends a relevant ID from the database to the end of the ID.Let's say the page has added 3 textboxes with the following IDs:

myTextBox1

myTextBox7

myTextBox115

Later,a javascript event fires,and I need to be able to access the control through JavaScript like this:

myJavaScriptFunction (controlID)

{
myvar = document.getElementById('myTextBox' + controlID);
}