throttle executes the function at most one time per wait period right?

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I want to throttle my function every 100 milliseconds. In the following code, I expect only 1 and 3 to be printed. But 2 is also printed in the actual result.

function say(what) {
  console.log(what);
}

const t = _.throttle(say, 100);

setTimeout(() => {
  t(1);
}, 50);
setTimeout(() => {
  t(1);
}, 50);
setTimeout(() => {
  t(1);
}, 50);
setTimeout(() => {
  t(1);
}, 55);
setTimeout(() => {
  t(2);
}, 55);
setTimeout(() => {
  t(3);
}, 500);
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.11.1/lodash.js"></script>

Your understanding of how you are using this throttle setup is not quite right.

To directly answer:

Shouldn't throttle execute the function at most one time per wait period?

With no options passed in, throttle will execute at the beginning and the end of the wait period (twice), provided the throttled function was called more than once in that period.

At 50ms your first function is called, and 'throttle' runs it immediately, also at this time your next f(1) is queued up to be called at 100ms. But then another f(1) is called, and another f(1) and then an f(2), and each new one replaces the last as the function to be called at 100ms (which is the time you've passed into throttle). Then over 100ms passes and then f(3) is called more or less when it should be.

If you don't pass any options into _.throttle it will immediately call the first function run (at 0ms) and then will call the last function run inside the set time period once that time elapses.

Using @zfrisch's code as a start:

function say(what) {
  console.log(what);
}

const t = _.throttle(say, 100);
const TO = (n, i) => setTimeout(() => {
  t(n);
}, i);

TO(1, 50); // logged immediately
TO(1, 50);
TO(1, 50);
TO(1, 55);
TO(2, 55); // logged at 100ms (as it was the last function attempted)
function say(what) {
  console.log(what);
}

const t = _.throttle(say, 100, { leading: false });
const TO = (n, i) => setTimeout(() => {
  t(n);
}, i);

TO(1, 50); // not logged at all
TO(1, 50);
TO(1, 50);
TO(1, 55);
TO(2, 55); // logged at 100ms (as it was the last function attempted)
function say(what) {
  console.log(what);
}

const t = _.throttle(say, 100, { trailing: false });
const TO = (n, i) => setTimeout(() => {
  t(n);
}, i);

TO(1, 50); // logged immediately
TO(1, 50);
TO(1, 50);
TO(1, 55);
TO(2, 55); // not logged at all

When should throttle execute your function? � Issue #170 , So throttle doesn't execute your function until after the wait period has elapsed. repeatedly, will only actually call the wrapped function at most dynamically, as the target throttled function doesn't yet exist at the time of the declaration. fires once immediately, and every N seconds thereafter and resets itself N seconds � Throttling will change the function in such a way that it can be fired at most once in a time interval. For instance, throttling will execute the function only one time in 1000 milliseconds, no matter how many times the user clicks the button.

Throttle will delay the execution by the wait time, but the function will still be called. In your example, it will happen like follows: 50ms after the script start the first 1 is logged, and at this moment throttle will start counting 100ms. Any call to t in this period will be delayed. After the 100ms passed, the last call made to t will be triggered. 100ms passes again and t is not called, so nothing happens, then the last call happens.

An ES6 implementation of the throttle function. "Throttling enforces a , "Throttling enforces a maximum number of times a function can be called over time. As in 'execute this function at most once every 100 milliseconds. function throttle(callback, wait, immediate = false) { execute immediately the first time it's invoked, unlike debounce , which waits until its idle time is exceeded before� By default, throttle will execute the function as soon as you call it for the first time, and, if you call it again any number of times during the wait period, as soon as that period is over. If you'd like to disable the leading-edge call, pass {leading: false}, and if you'd like to disable the execution on the trailing-edge, pass {trailing: false}.

Throttling and Debouncing in JavaScript, Throttling and debouncing give us control over the rate at which a function is called. They are You could got to a aisle, pick a product, and immediately pay it (and repeat for each product). Consider a callback that we want to execute on window resize. Most likely not. Each time the debounce waiting period lessens. Throttle Throttling enforces a maximum number of times a function can be called over time. For example, “execute this function at most once every 100 milliseconds.” In other words: By using

Debouncing and Throttling Explained Through Examples, We've broached this topic before, but this time, David is going to drive. Having a debounced or throttled version of our function is especially useful when Why not trigger the function execution immediately, so it behaves exactly as the By using _.throttle , we don't allow to our function to execute more than once every X � One way to think about this implementation of throttle is like a chaining debounce. Each time the debounce waiting period lessens. throttle has some interesting possibilities. For example, you could store all the ignored executions and run them all at the end in order. To conclude

The Difference Between Throttling and Debouncing, Throttling enforces a maximum number of times a function can be called over time. As in “execute this function at most once every 100 milliseconds.” Wait until the user stops resizing the window; Don't fire an ajax event until the user stops typing; Measure the scroll position of the page You're absolutely right, Jeremy T. requestAnimationFrame is a way of queuing a function to be executed in the browser at the optimal time for rendering performance. A function that is queued with requestAnimationFrame will fire in the next frame. The browser will work hard to ensure that there are 60 frames per second (60 fps).

Maximum task execution time. 1 year (constrained by the maximum execution time) Maximum time Step Functions keeps a task in the queue. 1 year (constrained by the maximum execution time) Maximum activity pollers per Amazon Resource Name (ARN) 1,000 pollers calling GetActivityTask per ARN.

Comments
  • The call to t(2) is the last call made during the first 100ms. It'll be called when the 100ms expires. If you add the current timestamp (Date.now()) to the log messages you'll see that the call to t(2) happens almost exactly 100ms after the first t(1) call.
  • The feels a lot like an XY problem. Mind sharing the exact issue instead of this vague representation?
  • @Pointy so the first function is called always, and only the subsequent functions are spread out by wait time. Is that right?
  • @techguy2000 unless you set trailing to false - _.throttle(say, 100, { trailing: false }); This would log 1 and then 3
  • alternatively, you could set leading to false and it would log 2 and then 3 and not log 1 at all
  • Didn't expect this to be so active. This really helps me understand what throttle is doing. Thanks!
  • Nice Answer! I didn't see your edit and put some polish on mine, but I like this! +1
  • From the documentation: Creates a throttled function that only invokes func at most once per every wait milliseconds - the function is not still called
  • @DerekPollard But per the lodash source code, leading and trailing are set to true github.com/lodash/lodash/blob/master/throttle.js. So the function is called immediately, 100ms later the most recent called function (in this case t(2)) is called, and then a little under 400ms later the final function is called
  • How does this contradict what I said? The function is still called not more the once per wait time. The call is delayed, but it happens at the end of the wait time. If you make 1000 calls spread over 1 second with wait time 100ms you will get the function invoked at most 10 times (11 if leading and trailing are true).