Wait until flag=true

Question

I have javascript function like this:

function myFunction(number) {

    var x=number;
    ...
    ... more initializations
    //here need to wait until flag==true
    while(flag==false)
    {}

    ...
    ... do something

}

The problem is that the javascript is stuck in the while and stuck my program. so my question is how can I wait in the middle of the function until flag is true without "busy-wait"?

Answer 1

Javascript is single threaded, hence the page blocking behaviour. You can use the deferred/promise approach suggested by others, but the most basic way would be to use window.setTimeout. E.g.

function checkFlag() {
    if(flag == false) {
       window.setTimeout(checkFlag, 100); /* this checks the flag every 100 milliseconds*/
    } else {
      /* do something*/
    }
}
checkFlag();

Here is a good tutorial with further explanation: Tutorial

EDIT

As others pointed out, the best way would be to re-structure your code to use callbacks. However, this answer should give you an idea how you can 'simulate' an asynchronous behaviour with window.setTimeout.