Add pqueue helper (untested)

pqueue.js

@@ -0,0 +1,35 @@
+const queryable = promise => {
+	let result = promise.then(result => {
+		q.result = result
+		q.done = true
+	}).catch(error => {
+		q.error = error
+		q.done = true
+	})
+	return result
+}
+
+export default () => {
+	const queue = []
+	const delayed = new Map()
+
+	loop = () => {
+		for (promise of queue.splice(0, queue.findIndex(promise => !promise.done))) {
+			if (promise.result) {
+				delayed.get(promise).resolve(promise.result)
+			} else if (promise.error) {
+				delayed.get(promise).reject(promise.error)
+			} else {
+				break
+			}
+		}
+	}
+
+	return promise => {
+		promise = queryable(promise)
+		queue.push(promise)
+		promise.finally(loop)
+		const result = new Promise(fulfill, reject => delayed.set(promise, {fulfill, reject}))
+		return result
+	}
+}