array.js

class Channel {
	constructor () {
		this.csm = []
		this.msg = []
	}

	enqueue (data) {
		this.msg.push(data)
		this.pass()
	}

	dequeue () {
		return new Promise(resolve => {
			let p = { resolve }
			this.csm.push(p)
			this.pass()
			setTimeout(() => {
				p.resolve = undefined
				resolve([undefined, 'timeout'])
			}, 500)
		})
	}

	pass () {
		if (this.csm.length == 0 || this.msg.length == 0) return
		var cons = this.csm.shift()

		/* ignore outdated consumer */
		if (!cons.resolve) {
			this.pass()
			return
		}

		var mess = this.msg.shift()
		cons([mess, undefined])
	}
}