How to check if a string is numeric or not

[minhhn0205]

Hi,
I would like to check if msg.payload (string) is a number or not.

If I don't use the function node, is there a node that can check this?
I tried searching in node-red library with keyword like verify, validate but no results.

Please tell me!
Thanks.

[Trying_to_learn]

switch node.

is of type from the selection type.

Then add another line to say if it is a number type.

[minhhn0205]

If using msg.payload ( string ) with the value 3, the type of is a string, not a number.

I'm thinking of using a Change node or a Switch node in combination with the regular expression.

[Trying_to_learn]

@minhhn0205

I would like to check if msg.payload ( string ) is a number or not.

If I don't use the function node, is there a node that can check this?
I tried searching in node-red library with keyword like verify, validate but no results.

I'm confused.

[softy2k]

Take a look at isNaN() Function

JavaScript isNaN() Function

[Colin]

To check whether the payload is a string containing only digits with an optional +/- you can use a Switch node configured with

That says that the string must be an optional + or - followed by one or more digits and nothing else. The node will pass valid strings and suppress anything else. If you want a notification of a non number then add an Otherwise case going to output 2.

[Edit] If you want to allow a single decimal point then it gets much more complex, so if you want that then a regex may not be the best solution.

[janvda]

@minhhn0205

I would like to check if msg.payload ( string ) is a number or not.

Here a jsonata expression which you can use in a switch node:

• https://try.jsonata.org/Rn5TyoG1h

/* checks if payload is a number or a string holding a number (no decimal or blanks !) */
$type(payload)="number" ? true : ( $type(payload)="string" and $match(payload,/^[0-9]+$/))

[minhhn0205]

Great, both ways work!!!
I have learned many things...
@Colin, @janvda Thank you very much!

[drmibell]

You might run into some edge cases trying to parse the string yourself, so I'd advise actually using Javascript or JSONata to do the test. These flows are examples.

[{"id":"136fdf3.4a09421","type":"inject","z":"5e0bf7b3.fc34d","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"1","payloadType":"str","x":150,"y":80,"wires":[["83f96ee6.f56a98"]]},{"id":"932a054.d90cb78","type":"inject","z":"5e0bf7b3.fc34d","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"a","payloadType":"str","x":150,"y":120,"wires":[["83f96ee6.f56a98"]]},{"id":"1fe64078.48d6","type":"inject","z":"5e0bf7b3.fc34d","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"0.10","payloadType":"str","x":150,"y":160,"wires":[["83f96ee6.f56a98"]]},{"id":"83f96ee6.f56a98","type":"link out","z":"5e0bf7b3.fc34d","name":"","links":["cb123243.5647c","394d8256.6de2fe"],"x":275,"y":120,"wires":[]},{"id":"cb123243.5647c","type":"link in","z":"5e0bf7b3.fc34d","name":"","links":["83f96ee6.f56a98"],"x":355,"y":80,"wires":[["b426a0ce.541b8"]]},{"id":"b426a0ce.541b8","type":"change","z":"5e0bf7b3.fc34d","name":"check","rules":[{"t":"set","p":"payload","pt":"msg","to":"$number(payload)","tot":"jsonata"}],"action":"","property":"","from":"","to":"","reg":false,"x":450,"y":80,"wires":[["53a7db7a.7cbda4"]]},{"id":"53a7db7a.7cbda4","type":"debug","z":"5e0bf7b3.fc34d","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"payload","targetType":"msg","statusVal":"","statusType":"auto","x":610,"y":80,"wires":[]},{"id":"61651499.efacf4","type":"catch","z":"5e0bf7b3.fc34d","name":"","scope":["b426a0ce.541b8"],"uncaught":false,"x":450,"y":120,"wires":[["b89cbecb.b9b3e8"]]},{"id":"ba32a239.3f7fd","type":"function","z":"5e0bf7b3.fc34d","name":"","func":"msg.payload = + msg.payload\nreturn msg;","outputs":1,"noerr":0,"initialize":"","finalize":"","x":460,"y":160,"wires":[["a9eb457f.bd7648"]]},{"id":"394d8256.6de2fe","type":"link in","z":"5e0bf7b3.fc34d","name":"","links":["83f96ee6.f56a98"],"x":355,"y":160,"wires":[["ba32a239.3f7fd"]]},{"id":"a9eb457f.bd7648","type":"debug","z":"5e0bf7b3.fc34d","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"payload","targetType":"msg","statusVal":"","statusType":"auto","x":610,"y":160,"wires":[]},{"id":"b89cbecb.b9b3e8","type":"debug","z":"5e0bf7b3.fc34d","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"error.message","targetType":"msg","statusVal":"","statusType":"auto","x":630,"y":120,"wires":[]}]

If you really need to avoid the function node, then ignore the second flow.