Add 'debounce' util

Author: gargrave

src/utils/debounce.spec.ts

@@ -0,0 +1,39 @@
+import '@testing-library/jest-dom/extend-expect'
+
+import { debounce } from './debounce'
+
+describe('debounce', () => {
+  beforeEach(() => {
+    jest.resetAllMocks()
+    jest.useFakeTimers()
+  })
+
+  it('returns a debounced function that only gets called after the specified period of time', () => {
+    const timeout = 100
+    const testName = 'Billy'
+    const testNum = 42
+    const fn = jest.fn((name: string, num: number) => `Hi ${name} ${num}`)
+    const debounced = debounce(fn, timeout)
+
+    expect(typeof debounced).toBe('function')
+    expect(fn).toHaveBeenCalledTimes(0)
+
+    debounced(testName, testNum)
+    expect(fn).toHaveBeenCalledTimes(0)
+
+    // calls a few times and advance timers by "less than timeout"
+    jest.advanceTimersByTime(10)
+    debounced(testName, testNum)
+    jest.advanceTimersByTime(20)
+    debounced(testName, testNum)
+    jest.advanceTimersByTime(timeout - 1)
+    expect(fn).toHaveBeenCalledTimes(0)
+
+    // now call, advance to timeout, and ensure it got called and returned correctly
+    debounced(testName, testNum)
+    jest.advanceTimersByTime(timeout)
+    expect(fn).toHaveBeenCalledTimes(1)
+    expect(fn).toHaveBeenLastCalledWith(testName, testNum)
+    expect(fn).toHaveReturnedWith('Hi Billy 42')
+  })
+})

src/utils/debounce.ts

@@ -0,0 +1,17 @@
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+export const debounce = (fn: (...args) => any, timeout: number) => {
+  const debounceTimeout = Math.max(timeout, 1)
+  let currentTimeout
+
+  return (...args) => {
+    if (currentTimeout) {
+      clearTimeout(currentTimeout)
+    }
+
+    return new Promise(resolve => {
+      currentTimeout = setTimeout(() => {
+        resolve(fn(...args))
+      }, debounceTimeout)
+    })
+  }
+}

src/utils/index.ts

@@ -1,3 +1,4 @@
 export * from './classNames'
+export * from './debounce'
 export * from './keycodes'
 export * from './wrap'