KEYVAL:
here is a label. This is where the execution jumps at the continue KEYVAL;
statement.
See the MDN on continue :
The continue statement can include an optional label that allows the program to jump to the next iteration of a labelled loop statement instead of the current loop. In this case, the continue statement needs to be nested within this labelled statement.
This is mostly used when you want to deal with nested loops as it lets you choose the loop level to which to jump. In your code, it looks useless, you can remove the label and keep a simple continue
statement.