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防抖和节流 (Debounce & Throttle)

Usage:

Some events like resize(), scroll(), keypress(), and mousemove() will frequently trigger callback functions that are bind to that event.

We can use Debounce and Throttle to reduce the frequency.


Application:

1) 防抖(Debounce)

    1>Search bar, only after input all the content then send request

    2>Validation of phone number, email

    3>Resize(), only after user finishes resizing will it compute the window size


2) 节流(Throttle)

    1> scroll to load

    2> search, search connection (搜索联想功能)


Definition:

防抖(Debounce): execute once within n seconds. If it trigger several times within n seconds, it only occurs once.

节流(Throttle): execute after n seconds. If it is triggered several times within n seconds, re-start counting.


Implementation:

1) Throttle

    1> Timestamp: Cannot execute before a certain time

function throttled1(fn, delay = 500) {
    let oldtime = Date.now()
    return function (...args) {
        let newtime = Date.now()
        if (newtime - oldtime >= delay) {
            fn.apply(null, args)
            oldtime = Date.now()
        }
    }
}


    2> setTimeout: set timer to be null, until it finishes previous function

function throttled2(fn, delay = 500) {
    let timer = null
    return function (...args) {
        if (!timer) {
            timer = setTimeout(() => {
                fn.apply(this, args)
                timer = null
            }, delay);
        }
    }
}

    3> Combine two together

function throttled(fn, delay) {
    let timer = null
    let starttime = Date.now()
    return function () {
        let curTime = Date.now() // 当前时间
        let remaining = delay - (curTime - starttime)  // 从上一次到现在，还剩下多少多余时间
        let context = this
        let args = arguments
        clearTimeout(timer)
        if (remaining <= 0) {
            fn.apply(context, args)
            starttime = Date.now()
        } else {
            timer = setTimeout(fn, remaining);
        }
    }
}


2) Debounce

    1> setTimeout, if trigger again, clear interval and then re-setTimeout

function debounce(func, wait) {
    let timeout;

    return function () {
        let context = this; // 保存this指向
        let args = arguments; // 拿到event对象

        clearTimeout(timeout)
        timeout = setTimeout(function(){
            func.apply(context, args)
        }, wait);
    }
}


    2> If want to apply function immediately

function debounce(func, wait, immediate) {

    let timeout;

    return function () {
        let context = this;
        let args = arguments;

        if (timeout) clearTimeout(timeout); // timeout 不为null
        if (immediate) {
            let callNow = !timeout; // 第一次会立即执行，以后只有事件执行后才会再次触发
            timeout = setTimeout(function () {
                timeout = null;
            }, wait)
            if (callNow) {
                func.apply(context, args)
            }
        }
        else {
            timeout = setTimeout(function () {
                func.apply(context, args)
            }, wait);
        }
    }
}


Third-Party Library: ahook

useDebounceFn:

const { run: tryLoadMore } = useDebounceFn(
() => {
console.log("try load more");
},
{
wait: 1000,
}
);


useDebounceEffect: 类似于useEffect, 但是加上了防抖

useDebounceEffect(
() => {
saveAction();
},
[componentList, pageInfo],
{ wait: 1000 }
);



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