How to extract characters using Javascript in a function?

[MercierFab]

Hello, I need to extract 2 characters from a payload (string) using substr(x,y) in a function node and it doesn't work. ex : var temperature = payload.substr(2,4). The function doesn't exist. Should I install a package or use an other function ? Do you have a tip? Or at least how to extract one character from a string?
I have Node red V1.3.2.
Thanks for the answer.

[JGKK]

Dont know if you just miss typed but:

@MercierFab

var temperature = payload.substr(2,4)

should be:

var temperature = msg.payload.substr(2,4);

as only using payload will give you not a function as you need to qualify the whole object path of a msg object property not just the key itself.

Johannes

[E1cid]

Also if you just want 2 characters it should be msg.payload.substr(2,2)

[MercierFab]

Thanks both of you for the answer it's clear, it works.

Fabrice