140 lines
5.1 KiB
JavaScript
140 lines
5.1 KiB
JavaScript
/* eslint-disable no-undefined,no-param-reassign,no-shadow */
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/**
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* Throttle execution of a function. Especially useful for rate limiting
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* execution of handlers on events like resize and scroll.
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*
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* @param {number} delay - A zero-or-greater delay in milliseconds. For event callbacks, values around 100 or 250 (or even higher)
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* are most useful.
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* @param {Function} callback - A function to be executed after delay milliseconds. The `this` context and all arguments are passed through,
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* as-is, to `callback` when the throttled-function is executed.
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* @param {object} [options] - An object to configure options.
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* @param {boolean} [options.noTrailing] - Optional, defaults to false. If noTrailing is true, callback will only execute every `delay` milliseconds
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* while the throttled-function is being called. If noTrailing is false or unspecified, callback will be executed
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* one final time after the last throttled-function call. (After the throttled-function has not been called for
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* `delay` milliseconds, the internal counter is reset).
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* @param {boolean} [options.noLeading] - Optional, defaults to false. If noLeading is false, the first throttled-function call will execute callback
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* immediately. If noLeading is true, the first the callback execution will be skipped. It should be noted that
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* callback will never executed if both noLeading = true and noTrailing = true.
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* @param {boolean} [options.debounceMode] - If `debounceMode` is true (at begin), schedule `clear` to execute after `delay` ms. If `debounceMode` is
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* false (at end), schedule `callback` to execute after `delay` ms.
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*
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* @returns {Function} A new, throttled, function.
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*/
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export function throttle(delay, callback, options) {
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const {
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noTrailing = false,
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noLeading = false,
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debounceMode = undefined,
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} = options || {};
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/*
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* After wrapper has stopped being called, this timeout ensures that
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* `callback` is executed at the proper times in `throttle` and `end`
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* debounce modes.
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*/
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let timeoutID;
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let cancelled = false;
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// Keep track of the last time `callback` was executed.
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let lastExec = 0;
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// Function to clear existing timeout
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function clearExistingTimeout() {
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if (timeoutID) {
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clearTimeout(timeoutID);
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}
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}
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// Function to cancel next exec
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function cancel(options) {
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const { upcomingOnly = false } = options || {};
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clearExistingTimeout();
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cancelled = !upcomingOnly;
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}
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/*
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* The `wrapper` function encapsulates all of the throttling / debouncing
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* functionality and when executed will limit the rate at which `callback`
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* is executed.
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*/
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function wrapper(...arguments_) {
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let self = this;
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let elapsed = Date.now() - lastExec;
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if (cancelled) {
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return;
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}
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// Execute `callback` and update the `lastExec` timestamp.
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function exec() {
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lastExec = Date.now();
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callback.apply(self, arguments_);
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}
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/*
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* If `debounceMode` is true (at begin) this is used to clear the flag
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* to allow future `callback` executions.
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*/
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function clear() {
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timeoutID = undefined;
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}
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if (!noLeading && debounceMode && !timeoutID) {
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/*
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* Since `wrapper` is being called for the first time and
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* `debounceMode` is true (at begin), execute `callback`
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* and noLeading != true.
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*/
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exec();
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}
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clearExistingTimeout();
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if (debounceMode === undefined && elapsed > delay) {
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if (noLeading) {
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/*
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* In throttle mode with noLeading, if `delay` time has
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* been exceeded, update `lastExec` and schedule `callback`
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* to execute after `delay` ms.
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*/
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lastExec = Date.now();
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if (!noTrailing) {
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timeoutID = setTimeout(debounceMode ? clear : exec, delay);
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}
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} else {
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/*
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* In throttle mode without noLeading, if `delay` time has been exceeded, execute
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* `callback`.
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*/
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exec();
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}
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} else if (noTrailing !== true) {
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/*
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* In trailing throttle mode, since `delay` time has not been
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* exceeded, schedule `callback` to execute `delay` ms after most
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* recent execution.
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*
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* If `debounceMode` is true (at begin), schedule `clear` to execute
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* after `delay` ms.
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*
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* If `debounceMode` is false (at end), schedule `callback` to
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* execute after `delay` ms.
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*/
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timeoutID = setTimeout(
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debounceMode ? clear : exec,
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debounceMode === undefined ? delay - elapsed : delay,
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);
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}
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}
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wrapper.cancel = cancel;
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// Return the wrapper function.
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return wrapper;
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}
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export function debounce(delay, callback, options) {
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const { atBegin = false } = options || {};
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return throttle(delay, callback, { debounceMode: atBegin !== false });
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}
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