Asked me to write a throttle function in javascript. Well, essentially...he wanted me to write a function that would call another function, but not if it had been called within a certain set time, which is essentially what a throttle function is. I completely flailed, but it's a useful function to have...probably why they put it in the underscore library which is what I based this answer on.

Question

Asked me to write a throttle function in javascript.  Well, essentially...he wanted me to write a function that would call another function, but not if it had been called within a certain set time, which is essentially what a throttle function is. I completely flailed, but it's a useful function to have...probably why they put it in the underscore library which is what I based this answer on.

Anónimo · Accepted Answer

/* var handle = setTimeout[myFunction, 5000);
     // Do this before it runs, and it'll never run
     clearTimeout(handle); */

    // async(queue calls) or sync(and throw calls away while executing)

    var lastTime = new Date().getTime();

    function foo() {

        var newTime = new Date().getTime();
        var gap = newTime - lastTime;
        console.log('foo called,  gap:' + gap);
        lastTime = newTime;
    }

    //Calls it immediately the first time and throttles it on subsequent calls
    //Non-queueing so calls during throttle period are ignored

    throttleFunction = function(func, wait) {
        var args, result;
        var timeout = null; //timeout call that acts as a flag
        var previous = 0;

        return function() {
            var now = new Date().getTime();
            var remaining = wait - (now - previous); //how much time is left on wait

            args = arguments; //just pass along the args
            if (remaining <= 0) {
                clearTimeout(timeout); //reset Timeout function call
                timeout = null; //reset timeout variable
                previous = now; //reset time so we know when the last time function was called
                result = func.apply(this, args);
                args = null; //reset args
            }
            return result;
        };
    };

    document.addEventListener("scroll", throttleFunction(foo, 2000));

Padawan · Answer

// Can't we just add a flag on the throttled function itself?

function fn() {
   console.log('run at', new Date().getTime());
}

function throttle(fn, delay) {
   if (!fn.lastRun || new Date().getTime() - fn.lastRun > delay) {
      fn.lastRun = new Date().getTime();
      return fn();
   } else
      console.log("wait");
}

document.addEventListener("scroll", throttle.bind(null, fn, delay));

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