What is this: main:for(...){...} doing?
- by David Murdoch
I pulled up the NWmatcher source code for some light morning reading and noticed this odd bit of code I'd never seen in javascript before:
main:for(/*irrelevant loop stuff*/){/*...*/}
This snippet can be found in the compileGroup method on line 441 (nwmatcher-1.1.1)
return new Function('c,s,d,h',
'var k,e,r,n,C,N,T,X=0,x=0;main:for(k=0,r=[];e=N=c[k];k++){' +
SKIP_COMMENTS + source +
'}return r;'
);
Now I figured out what main: is doing on my own. If you have a loop within a loop and want to skip to the next iteration of the outer loop (without completing the inner OR the outer loop) you can execute continue main. Example:
// This is obviously not the optimal way to find primes...
function getPrimes(max) {
var primes = [2], //seed
sqrt = Math.sqrt,
i = 3, j, s;
outer: for (; i <= max; s = sqrt(i += 2)) {
j = 3;
while (j <= s) {
if (i % j === 0) {
// if we get here j += 2 and primes.push(i) are
// not executed for the current iteration of i
continue outer;
}
j += 2;
}
primes.push(i);
}
return primes;
}
What is this called?
Are there any browsers that don't support it?
Are there other uses for it other than continue?
