import isObject from './isObject.js' 判斷變量是不是廣義的對象(對象、數組、函數), 不包括null跨域
正文
import isObject from'./isObject.js'/** * Creates a debounced function that delays invoking `func` until after `wait` * milliseconds have elapsed since the last time the debounced function was * invoked. The debounced function comes with a `cancel` method to cancel * delayed `func` invocations and a `flush` method to immediately invoke them. * Provide `options` to indicate whether `func` should be invoked on the * leading and/or trailing edge of the `wait` timeout. The `func` is invoked * with the last arguments provided to the debounced function. Subsequent * calls to the debounced function return the result of the last `func` * invocation. * * **Note:** If `leading` and `trailing` options are `true`, `func` is * invoked on the trailing edge of the timeout only if the debounced function * is invoked more than once during the `wait` timeout. * * If `wait` is `0` and `leading` is `false`, `func` invocation is deferred * until the next tick, similar to `setTimeout` with a timeout of `0`. * * See [David Corbacho's article](https://css-tricks.com/debouncing-throttling-explained-examples/) * for details over the differences between `debounce` and `throttle`. * * @since 0.1.0 * @category Function * @param {Function} func The function to debounce. * @param {number} [wait=0] The number of milliseconds to delay. * @param {Object} [options={}] The options object. * @param {boolean} [options.leading=false] * Specify invoking on the leading edge of the timeout. * @param {number} [options.maxWait] * The maximum time `func` is allowed to be delayed before it's invoked. * @param {boolean} [options.trailing=true] * Specify invoking on the trailing edge of the timeout. * @returns {Function} Returns the new debounced function. * @example * * // Avoid costly calculations while the window size is in flux. * jQuery(window).on('resize', debounce(calculateLayout, 150)) * * // Invoke `sendMail` when clicked, debouncing subsequent calls. * jQuery(element).on('click', debounce(sendMail, 300, { * 'leading': true, * 'trailing': false * })) * * // Ensure `batchLog` is invoked once after 1 second of debounced calls. * const debounced = debounce(batchLog, 250, { 'maxWait': 1000 }) * const source = new EventSource('/stream') * jQuery(source).on('message', debounced) * * // Cancel the trailing debounced invocation. * jQuery(window).on('popstate', debounced.cancel) * * // Check for pending invocations. * const status = debounced.pending() ? "Pending..." : "Ready" */functiondebounce(func, wait, options) {
let lastArgs,
lastThis,
maxWait,
result,
timerId,
lastCallTime
let lastInvokeTime = 0let leading = falselet maxing = falselet trailing = trueif (typeof func != 'function') {
thrownewTypeError('Expected a function')
}
wait = +wait || 0if (isObject(options)) {
leading = !!options.leading
maxing = 'maxWait'in options
maxWait = maxing ? Math.max(+options.maxWait || 0, wait) : maxWait
trailing = 'trailing'in options ? !!options.trailing : trailing
}
functioninvokeFunc(time) {
const args = lastArgs
const thisArg = lastThis
lastArgs = lastThis = undefined
lastInvokeTime = time
result = func.apply(thisArg, args)
return result
}
functionleadingEdge(time) {
// Reset any `maxWait` timer.
lastInvokeTime = time
// Start the timer for the trailing edge.
timerId = setTimeout(timerExpired, wait)
// Invoke the leading edge.return leading ? invokeFunc(time) : result
}
functionremainingWait(time) {
const timeSinceLastCall = time - lastCallTime
const timeSinceLastInvoke = time - lastInvokeTime
const timeWaiting = wait - timeSinceLastCall
return maxing
? Math.min(timeWaiting, maxWait - timeSinceLastInvoke)
: timeWaiting
}
functionshouldInvoke(time) {
const timeSinceLastCall = time - lastCallTime
const timeSinceLastInvoke = time - lastInvokeTime
// Either this is the first call, activity has stopped and we're at the// trailing edge, the system time has gone backwards and we're treating// it as the trailing edge, or we've hit the `maxWait` limit.return (lastCallTime === undefined || (timeSinceLastCall >= wait) ||
(timeSinceLastCall < 0) || (maxing && timeSinceLastInvoke >= maxWait))
}
functiontimerExpired() {
const time = Date.now()
if (shouldInvoke(time)) {
return trailingEdge(time)
}
// Restart the timer.
timerId = setTimeout(timerExpired, remainingWait(time))
}
functiontrailingEdge(time) {
timerId = undefined// Only invoke if we have `lastArgs` which means `func` has been// debounced at least once.if (trailing && lastArgs) {
return invokeFunc(time)
}
lastArgs = lastThis = undefinedreturn result
}
functioncancel() {
if (timerId !== undefined) {
clearTimeout(timerId)
}
lastInvokeTime = 0
lastArgs = lastCallTime = lastThis = timerId = undefined
}
functionflush() {
return timerId === undefined ? result : trailingEdge(Date.now())
}
functionpending() {
return timerId !== undefined
}
functiondebounced(...args) {
const time = Date.now()
const isInvoking = shouldInvoke(time)
lastArgs = args
lastThis = this
lastCallTime = time
if (isInvoking) {
if (timerId === undefined) {
return leadingEdge(lastCallTime)
}
if (maxing) {
// Handle invocations in a tight loop.
timerId = setTimeout(timerExpired, wait)
return invokeFunc(lastCallTime)
}
}
if (timerId === undefined) {
timerId = setTimeout(timerExpired, wait)
}
return result
}
debounced.cancel = cancel
debounced.flush = flush
debounced.pending = pending
return debounced
}
exportdefault debounce
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functiontrailingEdge(time) {
timerId = undefined// Only invoke if we have `lastArgs` which means `func` has been// debounced at least once.if (trailing && lastArgs) {
return invokeFunc(time)
}
lastArgs = lastThis = undefinedreturn result
}
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if (isInvoking) {
if (timerId === undefined) {
return leadingEdge(lastCallTime)
}
// **看這裏**，若是有maxWait那麼maxing就爲真if (maxing) {
// Handle invocations in a tight loop.
timerId = setTimeout(timerExpired, wait)
return invokeFunc(lastCallTime)
}
}
if (timerId === undefined) {
timerId = setTimeout(timerExpired, wait)
}
複製代碼
能夠看到remainingWait和shouldInvoke中也都對maxing進行了判斷
總結一下其實就是下面這樣
// throttle的簡單實現，定時器都沒用var throttle = function(wait, func){
var last = 0returnfunction(){
var time = +newDate()
if (time - last > wait){
func.apply(this, arguments)
last = curr
}
}
}
複製代碼
