A queue that handles async functions in order with a wait time between each callback.

async_queue.ts

/*
  Usage:
    import async_queue from 'async_queue'
    const queue = async_queue(<wait_time_in_ms>)
    queue(async () => await someSlowAction1())
    queue(async () => await someSlowAction2())
*/
export default (waitTime : number) => {
  const queue : Array<() => Promise<void>> = []
  return (callback : () => Promise<void>) => {
    // Add the new callback.
    queue.push(async () => {
      await callback()
      await new Promise(resolve => setTimeout(resolve, waitTime))
      // Unqueue and call the next callback.
      if (queue.length >= 1) {
        queue.shift()
        if (queue.length) {
          queue[0]()
        }
      }
    })
    // Run the current callback directly if it's the only element on the queue.
    if (queue.length == 1) {
      queue[0]()
    }
  }
}