If cell 1 or cell 2 is blank, then do this, else do this?

What would be the eqivilant google sheets formula to execute this logic

if(typeof A2:A === 'undefined' || typeof B2:B === 'undefined') {
    return "--"
} else {
    return A2:A - B2:B
}

So basically if cell A or cell B is blank using something like =ISBLANK(A2:A) then return the string "--", else return cell A minus cell B

This is what I tried with no luck.

=IF(ISBLANK(A2:A)|ISBLANK(B2:B), "--", A2:A-B2:B)

I noticed the | had no functionality, so I tried to use =OR() instead, but I couldn't use an else statement with =OR().