--- /dev/null
+var isObject = require('./isObject'),
+ now = require('./now'),
+ toNumber = require('./toNumber');
+
+/** Used as the `TypeError` message for "Functions" methods. */
+var FUNC_ERROR_TEXT = 'Expected a function';
+
+/* Built-in method references for those with the same name as other `lodash` methods. */
+var nativeMax = Math.max;
+
+/**
+ * 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 an options object 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 the debounced function is
+ * invoked more than once during the `wait` timeout.
+ *
+ * See [David Corbacho's article](http://drupalmotion.com/article/debounce-and-throttle-visual-explanation)
+ * for details over the differences between `_.debounce` and `_.throttle`.
+ *
+ * @static
+ * @memberOf _
+ * @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
+ * var debounced = _.debounce(batchLog, 250, { 'maxWait': 1000 });
+ * var source = new EventSource('/stream');
+ * jQuery(source).on('message', debounced);
+ *
+ * // cancel a trailing debounced invocation
+ * jQuery(window).on('popstate', debounced.cancel);
+ */
+function debounce(func, wait, options) {
+ var args,
+ maxTimeoutId,
+ result,
+ stamp,
+ thisArg,
+ timeoutId,
+ trailingCall,
+ lastCalled = 0,
+ leading = false,
+ maxWait = false,
+ trailing = true;
+
+ if (typeof func != 'function') {
+ throw new TypeError(FUNC_ERROR_TEXT);
+ }
+ wait = toNumber(wait) || 0;
+ if (isObject(options)) {
+ leading = !!options.leading;
+ maxWait = 'maxWait' in options && nativeMax(toNumber(options.maxWait) || 0, wait);
+ trailing = 'trailing' in options ? !!options.trailing : trailing;
+ }
+
+ function cancel() {
+ if (timeoutId) {
+ clearTimeout(timeoutId);
+ }
+ if (maxTimeoutId) {
+ clearTimeout(maxTimeoutId);
+ }
+ lastCalled = 0;
+ args = maxTimeoutId = thisArg = timeoutId = trailingCall = undefined;
+ }
+
+ function complete(isCalled, id) {
+ if (id) {
+ clearTimeout(id);
+ }
+ maxTimeoutId = timeoutId = trailingCall = undefined;
+ if (isCalled) {
+ lastCalled = now();
+ result = func.apply(thisArg, args);
+ if (!timeoutId && !maxTimeoutId) {
+ args = thisArg = undefined;
+ }
+ }
+ }
+
+ function delayed() {
+ var remaining = wait - (now() - stamp);
+ if (remaining <= 0 || remaining > wait) {
+ complete(trailingCall, maxTimeoutId);
+ } else {
+ timeoutId = setTimeout(delayed, remaining);
+ }
+ }
+
+ function flush() {
+ if ((timeoutId && trailingCall) || (maxTimeoutId && trailing)) {
+ result = func.apply(thisArg, args);
+ }
+ cancel();
+ return result;
+ }
+
+ function maxDelayed() {
+ complete(trailing, timeoutId);
+ }
+
+ function debounced() {
+ args = arguments;
+ stamp = now();
+ thisArg = this;
+ trailingCall = trailing && (timeoutId || !leading);
+
+ if (maxWait === false) {
+ var leadingCall = leading && !timeoutId;
+ } else {
+ if (!maxTimeoutId && !leading) {
+ lastCalled = stamp;
+ }
+ var remaining = maxWait - (stamp - lastCalled),
+ isCalled = remaining <= 0 || remaining > maxWait;
+
+ if (isCalled) {
+ if (maxTimeoutId) {
+ maxTimeoutId = clearTimeout(maxTimeoutId);
+ }
+ lastCalled = stamp;
+ result = func.apply(thisArg, args);
+ }
+ else if (!maxTimeoutId) {
+ maxTimeoutId = setTimeout(maxDelayed, remaining);
+ }
+ }
+ if (isCalled && timeoutId) {
+ timeoutId = clearTimeout(timeoutId);
+ }
+ else if (!timeoutId && wait !== maxWait) {
+ timeoutId = setTimeout(delayed, wait);
+ }
+ if (leadingCall) {
+ isCalled = true;
+ result = func.apply(thisArg, args);
+ }
+ if (isCalled && !timeoutId && !maxTimeoutId) {
+ args = thisArg = undefined;
+ }
+ return result;
+ }
+ debounced.cancel = cancel;
+ debounced.flush = flush;
+ return debounced;
+}
+
+module.exports = debounce;