Here is another example on what dceejay suggested
[{"id":"fe068816.7bb6f8","type":"tab","label":"HTML selector","disabled":false,"info":""},{"id":"7d11437a.bb6f5c","type":"inject","z":"fe068816.7bb6f8","name":"Go","topic":"","payload":"Go","payloadType":"str","repeat":"","crontab":"","once":false,"onceDelay":"","x":90,"y":160,"wires":[["5742f4b2.4ec27c"]]},{"id":"a3c9bfc2.02a27","type":"html","z":"fe068816.7bb6f8","name":"Select ","property":"payload","outproperty":"version","tag":"","ret":"text","as":"single","x":550,"y":180,"wires":[["4521a7e3.8680a8"]]},{"id":"1f91ed83.736b02","type":"http request","z":"fe068816.7bb6f8","name":"Endpoint","method":"GET","ret":"txt","url":"https://nodered.org","tls":"","proxy":"","x":420,"y":180,"wires":[["a3c9bfc2.02a27"]]},{"id":"4128fc36.94f324","type":"debug","z":"fe068816.7bb6f8","name":"","active":true,"tosidebar":true,"console":false,"tostatus":true,"complete":"version","targetType":"msg","x":810,"y":160,"wires":[]},{"id":"8c22c116.9ec0b","type":"debug","z":"fe068816.7bb6f8","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"select","targetType":"msg","x":310,"y":100,"wires":[]},{"id":"5742f4b2.4ec27c","type":"change","z":"fe068816.7bb6f8","name":"Valid selector","rules":[{"t":"set","p":"select","pt":"msg","to":".node-red-latest-version","tot":"str"}],"action":"","property":"","from":"","to":"","reg":false,"x":230,"y":160,"wires":[["1f91ed83.736b02","8c22c116.9ec0b"]]},{"id":"48ced238.6c645c","type":"inject","z":"fe068816.7bb6f8","name":"Go","topic":"","payload":"Go","payloadType":"str","repeat":"","crontab":"","once":false,"onceDelay":"","x":90,"y":220,"wires":[["ef26470e.0a9278"]]},{"id":"ef26470e.0a9278","type":"change","z":"fe068816.7bb6f8","name":"Invalid selector","rules":[{"t":"set","p":"select","pt":"msg","to":".node-red-latest-versio","tot":"str"}],"action":"","property":"","from":"","to":"","reg":false,"x":240,"y":220,"wires":[["1f91ed83.736b02","f56db6e.fd1ba48"]]},{"id":"f56db6e.fd1ba48","type":"debug","z":"fe068816.7bb6f8","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"select","targetType":"msg","x":310,"y":280,"wires":[]},{"id":"4521a7e3.8680a8","type":"switch","z":"fe068816.7bb6f8","name":"","property":"version","propertyType":"msg","rules":[{"t":"nempty"},{"t":"empty"}],"checkall":"true","repair":false,"outputs":2,"x":670,"y":180,"wires":[["4128fc36.94f324"],["a6f3dd93.fa76b"]]},{"id":"a6f3dd93.fa76b","type":"debug","z":"fe068816.7bb6f8","name":"","active":true,"tosidebar":true,"console":false,"tostatus":true,"complete":"version","targetType":"msg","x":810,"y":220,"wires":[]}]
Before I tried another approach, that was to check if the selector was included as a substring of the HTML response but came to the conclusion that it would be a bad idea.
