brightdata

gistfile1.txt

class Deferred {
	_resolved = null
	_rejected = null
	_cbs = []
	_errorCb = null

	then(cb) {
		if (!this._resolved) {
			this._cbs.push(cb)
		} else {
			cb(this._resolved)
		}

		return this
	}

	catch(cb) {
		this._errorCb = cb
	}

	reject(err) {
		if (!this._rejected) {
			this._rejected = err

			if (typeof this._errorCb === 'function') {
				this._errorCb(err)
			}
		}
	}

	resolve(res) {
		if (this._rejected) {
			return
		}

		if (!this._resolved) {
			if (this._cbs.length) {
				let cb = this._cbs.shift()

				let nextRes = res
				try {
					nextRes = cb(nextRes)
				} catch (err) {
					this.reject(err)
					return
				}

				if (nextRes instanceof Deferred) {
					nextRes.then(realNextRes => {
						this.resolve(realNextRes)
					})
				} else {
					this.resolve(nextRes)
				}
			} else {
				this._resolved = res
			}
		}
	}
}

const d = new Deferred()

d.then(res => {
	console.info('1, ', res)
	return 'a'
})

d.then(res => {
	let d1 = new Deferred()
	d1.then(res => {
		console.info('2, ', res)
		return 'c'
	})

	setTimeout(() => {
		d1.resolve('b')
	}, 2000)
	return d1
})

d.then(res => {
	throw new Error('Surprise!')
})

d.catch(err => {
	console.info(`Error: ${err.message}`)
})

d.resolve('hello')