Queue implementation in JavaScript

queue.js

class Queue {
  constructor (onTaskComplete) {
    this.tasks = []
    this.tasksCompleted = 0
    this.processing = false
    this.onTaskComplete = onTaskComplete || (() => {})
  }

  enqueue (task) {
    this.tasks.push(task)
    if (!this.processing) {
      this.process()
    }
  }

  dequeue () {
    return this.tasks.shift()
  }

  process () {
    if (!this.processing) {
      while (this.tasks.length > 0) {
        this.tryProcessNext()
      }
    }
  }

  tryProcessNext () {
    this.processing = true
    const task = this.dequeue()
    if (task) {
      if (typeof task === 'function') {
        task((result) => {
          this.tasksCompleted++
          this.onTaskComplete(result, this.tasksCompleted)
          this.processing = false
          this.process()
        })
      } else {
        this.tasksCompleted++
        this.onTaskComplete(task, this.tasksCompleted)
        this.processing = false
        this.process()
      }
    }
  }
}

w.example.js

const q = new Queue(res => console.log(res))

q.enqueue((next) => {
  next('task 1')
})

q.enqueue('task 2')

q.enqueue(next => {
  setTimeout(() => {
    next('task 3')
  }, 1000)
})


setTimeout(() => {
  q.enqueue('task 4')
}, 500)