92 lines
3.4 KiB
JavaScript
92 lines
3.4 KiB
JavaScript
|
/* eslint-disable no-undefined,no-param-reassign,no-shadow */
|
||
|
|
|
||
|
|
/**
|
||
|
|
* Throttle execution of a function. Especially useful for rate limiting
|
||
|
|
* execution of handlers on events like resize and scroll.
|
||
|
|
*
|
||
|
|
* @param {Number} delay A zero-or-greater delay in milliseconds. For event callbacks, values around 100 or 250 (or even higher) are most useful.
|
||
|
|
* @param {Boolean} [noTrailing] Optional, defaults to false. If noTrailing is true, callback will only execute every `delay` milliseconds while the
|
||
|
|
* throttled-function is being called. If noTrailing is false or unspecified, callback will be executed one final time
|
||
|
|
* after the last throttled-function call. (After the throttled-function has not been called for `delay` milliseconds,
|
||
|
|
* the internal counter is reset)
|
||
|
|
* @param {Function} callback A function to be executed after delay milliseconds. The `this` context and all arguments are passed through, as-is,
|
||
|
|
* to `callback` when the throttled-function is executed.
|
||
|
|
* @param {Boolean} [debounceMode] If `debounceMode` is true (at begin), schedule `clear` to execute after `delay` ms. If `debounceMode` is false (at end),
|
||
|
|
* schedule `callback` to execute after `delay` ms.
|
||
|
|
*
|
||
|
|
* @return {Function} A new, throttled, function.
|
||
|
|
*/
|
||
|
|
module.exports = function ( delay, noTrailing, callback, debounceMode ) {
|
||
|
|
|
||
|
|
// After wrapper has stopped being called, this timeout ensures that
|
||
|
|
// `callback` is executed at the proper times in `throttle` and `end`
|
||
|
|
// debounce modes.
|
||
|
|
var timeoutID;
|
||
|
|
|
||
|
|
// Keep track of the last time `callback` was executed.
|
||
|
|
var lastExec = 0;
|
||
|
|
|
||
|
|
// `noTrailing` defaults to falsy.
|
||
|
|
if ( typeof noTrailing !== 'boolean' ) {
|
||
|
|
debounceMode = callback;
|
||
|
|
callback = noTrailing;
|
||
|
|
noTrailing = undefined;
|
||
|
|
}
|
||
|
|
|
||
|
|
// The `wrapper` function encapsulates all of the throttling / debouncing
|
||
|
|
// functionality and when executed will limit the rate at which `callback`
|
||
|
|
// is executed.
|
||
|
|
function wrapper () {
|
||
|
|
|
||
|
|
var self = this;
|
||
|
|
var elapsed = Number(new Date()) - lastExec;
|
||
|
|
var args = arguments;
|
||
|
|
|
||
|
|
// Execute `callback` and update the `lastExec` timestamp.
|
||
|
|
function exec () {
|
||
|
|
lastExec = Number(new Date());
|
||
|
|
callback.apply(self, args);
|
||
|
|
}
|
||
|
|
|
||
|
|
// If `debounceMode` is true (at begin) this is used to clear the flag
|
||
|
|
// to allow future `callback` executions.
|
||
|
|
function clear () {
|
||
|
|
timeoutID = undefined;
|
||
|
|
}
|
||
|
|
|
||
|
|
if ( debounceMode && !timeoutID ) {
|
||
|
|
// Since `wrapper` is being called for the first time and
|
||
|
|
// `debounceMode` is true (at begin), execute `callback`.
|
||
|
|
exec();
|
||
|
|
}
|
||
|
|
|
||
|
|
// Clear any existing timeout.
|
||
|
|
if ( timeoutID ) {
|
||
|
|
clearTimeout(timeoutID);
|
||
|
|
}
|
||
|
|
|
||
|
|
if ( debounceMode === undefined && elapsed > delay ) {
|
||
|
|
// In throttle mode, if `delay` time has been exceeded, execute
|
||
|
|
// `callback`.
|
||
|
|
exec();
|
||
|
|
|
||
|
|
} else if ( noTrailing !== true ) {
|
||
|
|
// In trailing throttle mode, since `delay` time has not been
|
||
|
|
// exceeded, schedule `callback` to execute `delay` ms after most
|
||
|
|
// recent execution.
|
||
|
|
//
|
||
|
|
// If `debounceMode` is true (at begin), schedule `clear` to execute
|
||
|
|
// after `delay` ms.
|
||
|
|
//
|
||
|
|
// If `debounceMode` is false (at end), schedule `callback` to
|
||
|
|
// execute after `delay` ms.
|
||
|
|
timeoutID = setTimeout(debounceMode ? clear : exec, debounceMode === undefined ? delay - elapsed : delay);
|
||
|
|
}
|
||
|
|
|
||
|
|
}
|
||
|
|
|
||
|
|
// Return the wrapper function.
|
||
|
|
return wrapper;
|
||
|
|
|
||
|
|
};
|