Method chaining & task queue

LazyMan.js

class LazyManClass {
  constructor(name) {
    this.name = name
    this.tasks = []
    setTimeout(() => {
      this.flush()
    })
  }
  flush() {
    let seq = Promise.resolve()
    while(this.tasks.length) {
      const task = this.tasks.shift()
      seq = seq.then(task)
    }
  }
  appendTask(task) {
    this.tasks.push(task)
    return this
  }
  prependTask(task) {
    this.tasks.unshift(task)
    return this
  }
  sleep(time) {
    return this.appendTask(() => {
      console.log(`sleeping for ${time}ms`)
      return delay(time)
    })
  }
  sleepFirst(time) {
    return this.prependTask(() => {
      console.log(`sleeping for ${time}ms`)
      return delay(time)
    })
  }
  eat(food) {
    return this.appendTask(() => {
      console.log(`eating ${food}`)
    })
  }
  printLength() {
    return this.appendTask(() => {
      console.log(`tasks left: ${this.tasks.length}`)
    })
  }
}

function delay(time) {
  return new Promise((resolve) => {
    setTimeout(() => {
      resolve()
    }, time)
  })
}

function LazyMan(name) {
  return new LazyManClass(name)
}

LazyMan('Bob')
  .eat('fish')
  .appendTask(() => {
    console.log('start downloading')
    return delay(3000).then(() => {
      console.log('download completed')
    })
  })
  .eat('meat')
  .sleep(2000)
  .eat('apple')
  .sleepFirst(2000)
  .printLength()