How to execute a function before to call another function

April 22, 2022

I have a button with an onClick calling a function that unfortunately I can’t change. This function performs a login to the application:

<Button onClick={() => signIn()}>

but I need to execute some other code, to check if the user has checked a few checkboxes. Is there a way to call another function before the current one, and prevent the function call if the first one return false?

>Solution :

You can get the old onclick value, then replace it with your function that calls the original when it’s done checking.

let oldFunc = button.onclick;
button.onclick = function(event) {
    // code to check if the checkboxes are checked
    if (boxes_checked) {
        if (typeof oldFunc == 'string') {
            eval(oldFunc);
        } else {
            return oldFunc(event);
        }
    }
}