next.js/packages/next/src/server/node-environment-extensions/date.tsx

/**
 * We extend `Date` during builds and revalidates to ensure that prerenders don't observe the clock as a source of IO
 * When cacheComponents is enabled. The current time is a form of IO even though it resolves synchronously. When cacheComponents is
 * enabled we need to ensure that clock time is excluded from prerenders unless it is cached.
 *
 * There is tension here because time is used for both output and introspection. While arbitrary we intend to reserve
 * `Date` for output use cases and `performance` for introspection use cases. If you want to measure
 * how long something takes use `performance.timeOrigin` and `performance.now()` rather than `Date.now()` for instance.
 *
 * The extensions here never error nor alter the underlying Date objects, strings, and numbers created and thus should be transparent to callers.
 */
import { io } from './utils'

function createNow(originalNow: typeof Date.now) {
  return {
    now: function now() {
      io('`Date.now()`', 'time')
      return originalNow()
    },
  }['now'.slice() as 'now'].bind(null)
}

function createDate(originalConstructor: typeof Date): typeof Date {
  const properties = Object.getOwnPropertyDescriptors(originalConstructor)
  properties.now.value = createNow(originalConstructor.now)

  const apply = Reflect.apply
  const construct = Reflect.construct

  const newConstructor = Object.defineProperties(
    // Ideally this should not minify the name.
    function Date() {
      if (new.target === undefined) {
        io('`Date()`', 'time')
        return apply(originalConstructor, undefined, arguments)
      }
      if (arguments.length === 0) {
        io('`new Date()`', 'time')
      }
      return construct(originalConstructor, arguments, new.target)
    },
    properties
  )
  Object.defineProperty(originalConstructor.prototype, 'constructor', {
    value: newConstructor,
  })
  return newConstructor as typeof Date
}

try {
  // eslint-disable-next-line no-native-reassign
  Date = createDate(Date)
} catch {
  console.error(
    'Failed to install `Date` class extension. When using `experimental.cacheComponents`, APIs that read the current time will not correctly trigger dynamic behavior.'
  )
}