add hw2

node_modules/lodash-es/debounce.js

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+import isObject from './isObject.js';
+import now from './now.js';
+import toNumber from './toNumber.js';
+
+/** Error message constants. */
+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,
+    nativeMin = Math.min;
+
+/**
+ * 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 to 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`.
+ *
+ * @static
+ * @memberOf _
+ * @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.
+ * var debounced = _.debounce(batchLog, 250, { 'maxWait': 1000 });
+ * var source = new EventSource('/stream');
+ * jQuery(source).on('message', debounced);
+ *
+ * // Cancel the trailing debounced invocation.
+ * jQuery(window).on('popstate', debounced.cancel);
+ */
+function debounce(func, wait, options) {
+  var lastArgs,
+      lastThis,
+      maxWait,
+      result,
+      timerId,
+      lastCallTime,
+      lastInvokeTime = 0,
+      leading = false,
+      maxing = false,
+      trailing = true;
+
+  if (typeof func != 'function') {
+    throw new TypeError(FUNC_ERROR_TEXT);
+  }
+  wait = toNumber(wait) || 0;
+  if (isObject(options)) {
+    leading = !!options.leading;
+    maxing = 'maxWait' in options;
+    maxWait = maxing ? nativeMax(toNumber(options.maxWait) || 0, wait) : maxWait;
+    trailing = 'trailing' in options ? !!options.trailing : trailing;
+  }
+
+  function invokeFunc(time) {
+    var args = lastArgs,
+        thisArg = lastThis;
+
+    lastArgs = lastThis = undefined;
+    lastInvokeTime = time;
+    result = func.apply(thisArg, args);
+    return result;
+  }
+
+  function leadingEdge(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;
+  }
+
+  function remainingWait(time) {
+    var timeSinceLastCall = time - lastCallTime,
+        timeSinceLastInvoke = time - lastInvokeTime,
+        timeWaiting = wait - timeSinceLastCall;
+
+    return maxing
+      ? nativeMin(timeWaiting, maxWait - timeSinceLastInvoke)
+      : timeWaiting;
+  }
+
+  function shouldInvoke(time) {
+    var timeSinceLastCall = time - lastCallTime,
+        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));
+  }
+
+  function timerExpired() {
+    var time = now();
+    if (shouldInvoke(time)) {
+      return trailingEdge(time);
+    }
+    // Restart the timer.
+    timerId = setTimeout(timerExpired, remainingWait(time));
+  }
+
+  function trailingEdge(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 = undefined;
+    return result;
+  }
+
+  function cancel() {
+    if (timerId !== undefined) {
+      clearTimeout(timerId);
+    }
+    lastInvokeTime = 0;
+    lastArgs = lastCallTime = lastThis = timerId = undefined;
+  }
+
+  function flush() {
+    return timerId === undefined ? result : trailingEdge(now());
+  }
+
+  function debounced() {
+    var time = now(),
+        isInvoking = shouldInvoke(time);
+
+    lastArgs = arguments;
+    lastThis = this;
+    lastCallTime = time;
+
+    if (isInvoking) {
+      if (timerId === undefined) {
+        return leadingEdge(lastCallTime);
+      }
+      if (maxing) {
+        // Handle invocations in a tight loop.
+        clearTimeout(timerId);
+        timerId = setTimeout(timerExpired, wait);
+        return invokeFunc(lastCallTime);
+      }
+    }
+    if (timerId === undefined) {
+      timerId = setTimeout(timerExpired, wait);
+    }
+    return result;
+  }
+  debounced.cancel = cancel;
+  debounced.flush = flush;
+  return debounced;
+}
+
+export default debounce;