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191 lines
6.0 KiB
191 lines
6.0 KiB
var isObject = require('./isObject'),
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now = require('./now'),
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toNumber = require('./toNumber');
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/** Error message constants. */
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var FUNC_ERROR_TEXT = 'Expected a function';
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/* Built-in method references for those with the same name as other `lodash` methods. */
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var nativeMax = Math.max,
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nativeMin = Math.min;
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/**
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* Creates a debounced function that delays invoking `func` until after `wait`
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* milliseconds have elapsed since the last time the debounced function was
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* invoked. The debounced function comes with a `cancel` method to cancel
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* delayed `func` invocations and a `flush` method to immediately invoke them.
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* Provide `options` to indicate whether `func` should be invoked on the
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* leading and/or trailing edge of the `wait` timeout. The `func` is invoked
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* with the last arguments provided to the debounced function. Subsequent
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* calls to the debounced function return the result of the last `func`
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* invocation.
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*
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* **Note:** If `leading` and `trailing` options are `true`, `func` is
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* invoked on the trailing edge of the timeout only if the debounced function
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* is invoked more than once during the `wait` timeout.
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*
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* If `wait` is `0` and `leading` is `false`, `func` invocation is deferred
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* until to the next tick, similar to `setTimeout` with a timeout of `0`.
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*
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* See [David Corbacho's article](https://css-tricks.com/debouncing-throttling-explained-examples/)
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* for details over the differences between `_.debounce` and `_.throttle`.
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*
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* @static
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* @memberOf _
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* @since 0.1.0
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* @category Function
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* @param {Function} func The function to debounce.
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* @param {number} [wait=0] The number of milliseconds to delay.
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* @param {Object} [options={}] The options object.
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* @param {boolean} [options.leading=false]
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* Specify invoking on the leading edge of the timeout.
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* @param {number} [options.maxWait]
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* The maximum time `func` is allowed to be delayed before it's invoked.
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* @param {boolean} [options.trailing=true]
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* Specify invoking on the trailing edge of the timeout.
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* @returns {Function} Returns the new debounced function.
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* @example
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*
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* // Avoid costly calculations while the window size is in flux.
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* jQuery(window).on('resize', _.debounce(calculateLayout, 150));
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*
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* // Invoke `sendMail` when clicked, debouncing subsequent calls.
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* jQuery(element).on('click', _.debounce(sendMail, 300, {
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* 'leading': true,
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* 'trailing': false
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* }));
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*
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* // Ensure `batchLog` is invoked once after 1 second of debounced calls.
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* var debounced = _.debounce(batchLog, 250, { 'maxWait': 1000 });
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* var source = new EventSource('/stream');
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* jQuery(source).on('message', debounced);
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*
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* // Cancel the trailing debounced invocation.
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* jQuery(window).on('popstate', debounced.cancel);
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*/
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function debounce(func, wait, options) {
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var lastArgs,
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lastThis,
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maxWait,
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result,
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timerId,
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lastCallTime,
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lastInvokeTime = 0,
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leading = false,
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maxing = false,
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trailing = true;
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if (typeof func != 'function') {
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throw new TypeError(FUNC_ERROR_TEXT);
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}
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wait = toNumber(wait) || 0;
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if (isObject(options)) {
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leading = !!options.leading;
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maxing = 'maxWait' in options;
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maxWait = maxing ? nativeMax(toNumber(options.maxWait) || 0, wait) : maxWait;
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trailing = 'trailing' in options ? !!options.trailing : trailing;
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}
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function invokeFunc(time) {
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var args = lastArgs,
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thisArg = lastThis;
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lastArgs = lastThis = undefined;
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lastInvokeTime = time;
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result = func.apply(thisArg, args);
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return result;
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}
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function leadingEdge(time) {
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// Reset any `maxWait` timer.
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lastInvokeTime = time;
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// Start the timer for the trailing edge.
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timerId = setTimeout(timerExpired, wait);
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// Invoke the leading edge.
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return leading ? invokeFunc(time) : result;
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}
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function remainingWait(time) {
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var timeSinceLastCall = time - lastCallTime,
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timeSinceLastInvoke = time - lastInvokeTime,
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timeWaiting = wait - timeSinceLastCall;
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return maxing
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? nativeMin(timeWaiting, maxWait - timeSinceLastInvoke)
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: timeWaiting;
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}
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function shouldInvoke(time) {
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var timeSinceLastCall = time - lastCallTime,
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timeSinceLastInvoke = time - lastInvokeTime;
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// Either this is the first call, activity has stopped and we're at the
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// trailing edge, the system time has gone backwards and we're treating
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// it as the trailing edge, or we've hit the `maxWait` limit.
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return (lastCallTime === undefined || (timeSinceLastCall >= wait) ||
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(timeSinceLastCall < 0) || (maxing && timeSinceLastInvoke >= maxWait));
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}
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function timerExpired() {
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var time = now();
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if (shouldInvoke(time)) {
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return trailingEdge(time);
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}
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// Restart the timer.
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timerId = setTimeout(timerExpired, remainingWait(time));
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}
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function trailingEdge(time) {
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timerId = undefined;
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// Only invoke if we have `lastArgs` which means `func` has been
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// debounced at least once.
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if (trailing && lastArgs) {
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return invokeFunc(time);
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}
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lastArgs = lastThis = undefined;
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return result;
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}
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function cancel() {
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if (timerId !== undefined) {
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clearTimeout(timerId);
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}
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lastInvokeTime = 0;
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lastArgs = lastCallTime = lastThis = timerId = undefined;
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}
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function flush() {
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return timerId === undefined ? result : trailingEdge(now());
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}
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function debounced() {
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var time = now(),
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isInvoking = shouldInvoke(time);
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lastArgs = arguments;
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lastThis = this;
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lastCallTime = time;
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if (isInvoking) {
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if (timerId === undefined) {
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return leadingEdge(lastCallTime);
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}
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if (maxing) {
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// Handle invocations in a tight loop.
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clearTimeout(timerId);
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timerId = setTimeout(timerExpired, wait);
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return invokeFunc(lastCallTime);
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}
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}
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if (timerId === undefined) {
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timerId = setTimeout(timerExpired, wait);
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}
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return result;
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}
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debounced.cancel = cancel;
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debounced.flush = flush;
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return debounced;
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}
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module.exports = debounce;
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