How can I check if a JS file has been included already?

Question

I have split my javascript in different files. I want to prevent, that javascript files are loaded twice. How can I do that?

Answer 1

Not using any framework (that I know of), you can only do so by checking if a certain variable in the global scope has already been declared.

You could declare a variable var include1 = true; inside include1.js, and do something like

if (window.include1 !== true) {
    // load file dynamically
}