Sometimes there is 3rd party code to wait for and you can't hack into it with callbacks or promises. This script runs a check function periodically until it returns true (in which case its returned promise is resolved) or until it times out (which means it's going to reject). Inspired by a blog post by David Walsh.

poll.ts

/**
 * Resolve a promise when a condition matches
 *
 * @param condition The callback to run for checking
 * @param interval How frequent to check the condition (interval in milliseconds)
 * @param timeout After how many milliseconds to reject the promise
 */
async function poll(condition: () => boolean, interval: number, timeout?: number): Promise<void> {
  const startTime = Date.now()

  while (true) {
    if (typeof timeout === 'number' && Date.now() > startTime + timeout) {
      throw new Error('Condition not met before timeout')
    }

    const result = await condition()

    if (result) return

    await new Promise(resolve => setTimeout(resolve, interval))
  }
}