Unknown JavaScript syntax before for…in

Question

I am reading a book about single-page applications and at some point there is this for...in loop:

KEYVAL:
for(key_name in arg_map){
    if(arg_map.hasOwnProp         


        

Answer 1

It is a label, sort of a line-number but not locked to a line position.

Continue jumps to this label like a GOTO.

When this criteria is furfilled:

if(key_name.indexOf('_') === 0) continue KEYVAL;

JavaScript continues from that label above.