Remove meta refresh on task page, use JS to poll

app/static/polltask.js

@@ -0,0 +1,56 @@
+function getJSON(url, method) {
+	return new Promise(function(resolve, reject) {
+		fetch(new Request(url, {
+			method: method || "get",
+			credentials: "same-origin",
+			headers: {
+				"Accept": "application/json",
+			},
+		})).then(function(response) {
+			response.text().then(function(txt) {
+				resolve(JSON.parse(txt))
+			}).catch(reject)
+		}).catch(reject)
+	})
+}
+
+function pollTask(poll_url, disableTimeout) {
+	return new Promise(function(resolve, reject) {
+		var tries = 0;
+		function retry() {
+			tries++;
+			if (!disableTimeout && tries > 10) {
+				reject("timeout")
+			} else {
+				const interval = Math.min(tries*100, 1000)
+				console.log("Polling task in " + interval + "ms")
+				setTimeout(step, interval)
+			}
+		}
+		function step() {
+			getJSON(poll_url).then(function(res) {
+				if (res.status == "SUCCESS") {
+					console.log("Got result")
+					resolve(res.result)
+				} else {
+					retry()
+				}
+			}).catch(retry)
+		}
+		retry()
+	})
+}
+
+
+function performTask(url) {
+	return new Promise(function(resolve, reject) {
+		getJSON(url, "post").then(function(startResult) {
+			console.log(startResult)
+			if (typeof startResult.poll_url == "string") {
+				pollTask(startResult.poll_url).then(resolve).catch(reject)
+			} else {
+				reject("Start task didn't return string!")
+			}
+		}).catch(reject)
+	})
+}