Debounce with an exit timeout

debounce-with-exit.js

/**
 * Create a function that accepts a function and then
 * fires only after it hasn't been called for 250ms
 * 
 * Once that is done, create an "exit" functionality
 * that will take an "exit" number, higher than the 
 * "wait" variable, that will call the function regardless
 */

// params - fn, @{Callback}, wait @{Integer}
function debounce(fn, wait, exit) {
  let timeout;
  let called;
  let originalTimestamp;
  let timeSinceCalled;

  return function() {
    const functionCall = () => fn.apply(this, arguments);
    if (!called) {
      called = true;
      originalTimestamp = Date.now();
    } else {
      timeSinceCalled = Date.now() - originalTimestamp;
    }

    // is the amount of wait milliseconds higher than the milliseconds left to exit?
      // if true, set exit as variable to call timeout
      // if false, set wait as timeout

    const timeoutStamp = called && exit - timeSinceCalled < wait ? exit - timeSinceCalled : wait;
    
    clearTimeout(timeout);
    timeout = setTimeout(function() {
      timeSinceCalled = 0;
      called = false;
      functionCall();      
    }, timeoutStamp);
  }
}

const debounced = debounce(function() {
  console.log('hello world');
}, 250, 750);

debounced();
debounced();
debounced();
debounced();
debounced();
setTimeout(debounced, 240);
setTimeout(debounced, 240 * 2);
setTimeout(debounced, 240 * 3);
setTimeout(debounced, 240 * 4);
setTimeout(debounced, 240 * 5);
setTimeout(debounced, 240 * 6);
setTimeout(debounced, 240 * 7);
setTimeout(debounced, 240 * 8);
setTimeout(debounced, 240 * 9);
setTimeout(debounced, 240 * 10);
setTimeout(debounced, 240 * 11);