miscoded

This snippet is brought to you by Yahoo!Japan blogs. Quiz of the day: what is the RegExp meant to do and why does it fail?

if(img.match(/(.[jJ][pP][eE]?[gG]|.[gG][iI][fF]|.[pP][nN][gG])/)) {
return true;
}
return false;

(Yes, the variable name is a hint.)