var regex1 = /a/,
regex2 = /b/,
regex3 = /c/,
samplestring = 'b';
switch (true) {
case regex1.test(samplestring):
console.log("regex1");
break;
case regex2.test(samplestring):
console.log("regex2");
break;
case regex3.test(samplestring):
console.log("regex3");
break;
}