A debounce

README.md

@@ -399,3 +399,4 @@ This package provides a number of utility functions.
 | `removePhoneNumberCountryPrefix(phoneNumber, [, prefix])` | Removes a country prefix from a phone number based on the station config `country_code`. |
 | `onLocalStorageChange(key, callback)`                     | Calls `callback` when the value of `key` in `localStorage` changes.                      |
 | `decodeRadioToken(token)`                                 | Decodes a JWT radio token.                                                               |
+| `debounce(ms, fn)`                                        | Returns a debounced version of `fn` that delays invocation until `ms` after the last call. |

src/__test__/utils/debounce.test.js

@@ -0,0 +1,60 @@
+import { describe, expect, test, jest } from '@jest/globals'
+import debounce from '../../utils/debounce.js'
+
+describe('debounce', () => {
+  beforeEach(() => {
+    jest.useFakeTimers()
+  })
+
+  afterEach(() => {
+    jest.useRealTimers()
+  })
+
+  test('it calls the function after the delay', () => {
+    const fn = jest.fn()
+    const debounced = debounce(100, fn)
+
+    debounced()
+    expect(fn).not.toHaveBeenCalled()
+
+    jest.advanceTimersByTime(100)
+    expect(fn).toHaveBeenCalledTimes(1)
+  })
+
+  test('it resets the timer on subsequent calls', () => {
+    const fn = jest.fn()
+    const debounced = debounce(100, fn)
+
+    debounced()
+    jest.advanceTimersByTime(50)
+    debounced()
+    jest.advanceTimersByTime(50)
+
+    expect(fn).not.toHaveBeenCalled()
+
+    jest.advanceTimersByTime(50)
+    expect(fn).toHaveBeenCalledTimes(1)
+  })
+
+  test('it passes arguments to the function', () => {
+    const fn = jest.fn()
+    const debounced = debounce(100, fn)
+
+    debounced('hello', 42)
+    jest.advanceTimersByTime(100)
+
+    expect(fn).toHaveBeenCalledWith('hello', 42)
+  })
+
+  test('it uses the arguments from the last call', () => {
+    const fn = jest.fn()
+    const debounced = debounce(100, fn)
+
+    debounced('first')
+    debounced('second')
+    jest.advanceTimersByTime(100)
+
+    expect(fn).toHaveBeenCalledTimes(1)
+    expect(fn).toHaveBeenCalledWith('second')
+  })
+})

src/index.js

@@ -25,3 +25,4 @@ export { cdnImageUrl, cdnUrl } from './utils/cdnUrl.js'
 export { removePhoneNumberCountryPrefix } from './utils/phoneNumber.js'
 export { setupAirbrake, gtmFilter } from './utils/setupAirbrake.js'
 export { onLocalStorageChange } from './utils/onLocalStorageChange.js'
+export { default as debounce } from './utils/debounce.js'

src/utils/debounce.js

@@ -0,0 +1,7 @@
+export default function debounce(ms, fn) {
+  let timer
+  return (...args) => {
+    clearTimeout(timer)
+    timer = setTimeout(() => fn(...args), ms)
+  }
+}