From 879a69fd74c299c3ca2f0bf5421a1a7245ec2554 Mon Sep 17 00:00:00 2001
From: suressk <sure_ssk@outlook.com>
Date: Fri, 22 Jul 2022 22:22:56 +0800
Subject: [PATCH] feat: add `throttle`

---
 src/throttle.ts | 148 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 148 insertions(+)
 create mode 100644 src/throttle.ts

diff --git a/src/throttle.ts b/src/throttle.ts
new file mode 100644
index 0000000..96c138e
--- /dev/null
+++ b/src/throttle.ts
@@ -0,0 +1,148 @@
+export interface Options {
+  /**
+   * 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).
+   */
+  noTrailing?: boolean
+  /**
+   * Optional, defaults to false. If noLeading is false, the first throttled-function call will execute callback
+   * immediately. If noLeading is true, the first the callback execution will be skipped. It should be noted that
+   * callback will never executed if both noLeading = true and noTrailing = true.
+   */
+  noLeading?: number
+  /**
+   * 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.
+   */
+  debounceMode?: any
+}
+
+/**
+ * Throttle execution of a function. Especially useful for rate limiting
+ * execution of handlers on events like resize and scroll.
+ *
+ * @param {Function} callback - invoke func
+ * @param {number} delay - delay to be invoked time(ms)
+ * @param {Options} [options] - An object to configure options.
+ * @returns {Function} A new throttled function.
+ */
+function throttle<Args extends any[], F extends (...args: Args) => any>(
+  callback: F,
+  delay: number,
+  options: Options = {}
+): Function {
+  const {
+    noTrailing = false,
+    noLeading = false,
+    debounceMode = undefined
+  } = options
+  /*
+   * After wrapper has stopped being called, this timeout ensures that
+   * `callback` is executed at the proper times in `throttle` and `end`
+   * debounce modes.
+   */
+  let timerId: NodeJS.Timeout | number | null = null
+  let cancelled = false
+
+  // Keep track of the last time `callback` was executed.
+  let lastExec = 0
+
+  // Function to clear existing timeout
+  function clearExistingTimeout() {
+    if (timerId) {
+      clearTimeout(timerId)
+      timerId = null
+    }
+  }
+
+  // Function to cancel next exec
+  function cancel(options: { upcomingOnly?: boolean } = {}) {
+    const { upcomingOnly = false } = options
+    clearExistingTimeout()
+    cancelled = !upcomingOnly
+  }
+
+  /*
+   * The `wrapper` function encapsulates all of the throttling / debouncing
+   * functionality and when executed will limit the rate at which `callback`
+   * is executed.
+   */
+  function wrapper(this: any, ...args: Args) {
+    const self = this
+    const elapsed = Date.now() - lastExec
+
+    if (cancelled) {
+      return
+    }
+
+    // Execute `callback` and update the `lastExec` timestamp.
+    function exec() {
+      lastExec = Date.now()
+      callback.apply(self, args)
+    }
+
+    /*
+     * If `debounceMode` is true (at begin) this is used to clear the flag
+     * to allow future `callback` executions.
+     */
+    function clear() {
+      timerId = null
+    }
+
+    if (!noLeading && debounceMode && !timerId) {
+      /*
+       * Since `wrapper` is being called for the first time and
+       * `debounceMode` is true (at begin), execute `callback`
+       * and noLeading != true.
+       */
+      exec()
+    }
+
+    clearExistingTimeout()
+
+    if (debounceMode === undefined && elapsed > delay) {
+      if (noLeading) {
+        /*
+         * In throttle mode with noLeading, if `delay` time has
+         * been exceeded, update `lastExec` and schedule `callback`
+         * to execute after `delay` ms.
+         */
+        lastExec = Date.now()
+        if (!noTrailing) {
+          timerId = setTimeout(debounceMode ? clear : exec, delay)
+        }
+      } else {
+        /*
+         * In throttle mode without noLeading, 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.
+       */
+      timerId = setTimeout(
+        debounceMode ? clear : exec,
+        debounceMode === undefined ? delay - elapsed : delay
+      )
+    }
+  }
+
+  wrapper.cancel = cancel
+
+  // Return the wrapper function.
+  return wrapper
+}
+
+export default throttle