将 Javascript Function 作为参数传递 - 这个逻辑如何工作？

Question

I don't understand how the responseHandler function below is receiving a response from an API call, after a payment form submission. Here is a brief summary of the code:

var PaymentThing = function(e) {
    this["clientCallback"] = e;

    return {
        createToken: function() {
            // HTTP GET URL is generated and then an HTML script element is appended to the page head
            var a = "https://example.com/securitytoken?creditcard=xxxx?callback=PaymentThing.callback";
            var f = document.createElement("script");
            f.src = a;
            document.getElementsByTagName("head")[0].appendChild(f)
        },
        callback: function(e) {
            this["clientCallback"](e.status, e.results)
        }
    }
}


var responseHandler = function(status, response) {
    // How does this even work?
    console.log(response, status);
}


// Form Submission
jQuery('#checkout_payment_form').submit(function() {
    PaymentThing.createToken(responseHandler);
}

So my question is, how does the responseHandler function receive the response from the HTTP GET call? It looks to me like the HTTP call isn't even being made. I only see a URL being added to an HTML script element (with the createToken function), with the URL never even being called/executed (but somehow it is?). Also, how are the (status, response) parameters passed into the responseHandler function when I don't see them being passed into a responseHandler function call?

I don't understand the logic or order of operations here, can anyone please explain what's going on?

EDIT: Ok I think I see now how the responseHandler function is receiving the status and response parameters. I edited the code above to show there's a callback function in the generated HTTP url. But still, how is that URL being called? It still looks to me like it's inert and being stuck into the HTML of the page and not activating.

Answer 1

I think if you run the responseHandler function and store the result in a variable that can be called as a parameter in the PaymentThing.createToken() it will take it in consideration.

Answer 2

None of the code there calls responseHandler . There is no point in passing it to the createToken method as it completely ignores all the arguments.

It is possible that the script which is added to the page attempts to call a global function named responseHandler , but there's no way to tell without inspecting the script.