Check if javascript is already attached to a page?

Question

Is there any way to check if javascript file is already attached to the page by its file name.

For eg :

if ("path-to-script/scriptname.js") already embeded
{
call related function
}
else
{
Append '<script src="path-to-script/scriptname.js" type="text/javascript"> </script> '
call related function
}

Basically I dont want 1 script to be attached twice on the same page.

Answer 1

You might not always know what objects or functions a script contains in advance, in such cases you can search for script tags containing the desired src.

With jquery:

$("script[src*='"+scriptName+"']");

Without jquery:

document.querySelector("script[src*='"+scriptName+"']");

Answer 2

You'd need to test whether the actual function from the script file exists, like this:

if (window.function_name) {
    // script loaded
} else {
    // script not loaded
}

Answer 3

I agree with @zathrus though I think you should be using requirejs for things like this. The idea is that dependencies must be fetched before executing the code. The above method you are using may work but you can not guarantee anything.

RequireJS will beautifully maintain all the dependency loading. It is very easy to learn as well.