Question

I would like to know IF and HOW it is possible to write a function which observes an other function.
More precisely, the obsever keeps track of the the observed function execution time, and in case the latter exceeds a given time value, the observer function stop it.

So, briefly:

function observed() { // ... }

/**
 * Run a function and stop if this exceeds a given time.
 *
 * @param {Function} observedFunc The function to run and observe.
 * @param {Number} maxTime The maximum elapsed time allowed.
 */
function observer(observedFunc, maxTime) {
   /*
    * if (observedFunc exceed the time) 
    *     stop observedFunc;
    *     return;
    * else
    *     return; (when the observed function return)
    */
}

Is it possible to afford this, without changing the observed function?

Answer 1

Only with Web Workers in browsers that support it. If you ran observed from withing a Web Worker, then the main script could call terminate() on the worker.

Normally (at least historically) Javascript is single threaded, and so while observed is running, observer has no way of stopping it.