Question

As the question says, I am developing a custom asp.net control and I need to let the user know somehow that it needs a couple of JS libraries to be referenced on the page.

What is the best way to do this?

Answer 1

Check for the existence of the required libraries once the DOM is fully loaded:

function init() {
    if(!jQuery) {
        alert('This control requires jQuery');
    }
}

window.onload = init;

The above code will give you the idea. Modify to suit your needs.