Call An Asynchronous Javascript Function Synchronously

Question

First, this is a very specific case of doing it the wrong way on-purpose to retrofit an asynchronous call into a very synchronous codebase that is many thousands of lines lo

Answer 1

"don't tell me about how I should just do it "the right way" or whatever"

OK. _{^{but you should really do it the right way... or whatever}}

" I need a concrete example of how to make it block ... WITHOUT freezing the UI. If such a thing is possible in JS."

No, it is impossible to block the running JavaScript without blocking the UI.

Given the lack of information, it's tough to offer a solution, but one option may be to have the calling function do some polling to check a global variable, then have the callback set data to the global.

function doSomething() {

      // callback sets the received data to a global var
  function callBack(d) {
      window.data = d;
  }
      // start the async
  myAsynchronousCall(param1, callBack);

}

  // start the function
doSomething();

  // make sure the global is clear
window.data = null

  // start polling at an interval until the data is found at the global
var intvl = setInterval(function() {
    if (window.data) { 
        clearInterval(intvl);
        console.log(data);
    }
}, 100);

All of this assumes that you can modify doSomething(). I don't know if that's in the cards.

If it can be modified, then I don't know why you wouldn't just pass a callback to doSomething() to be called from the other callback, but I better stop before I get into trouble. ;)

---

Oh, what the heck. You gave an example that suggests it can be done correctly, so I'm going to show that solution...

function doSomething( func ) {

  function callBack(d) {
    func( d );
  }

  myAsynchronousCall(param1, callBack);

}

doSomething(function(data) {
    console.log(data);
});

Because your example includes a callback that is passed to the async call, the right way would be to pass a function to doSomething() to be invoked from the callback.

Of course if that's the only thing the callback is doing, you'd just pass func directly...

myAsynchronousCall(param1, func);