Test whether "num" is prime slowly (vie regexp match) and report runtime

isPrime.js

// GatewayScript script (IBM DataPower Gateways) that tests passed
// number "num" for being a prime slowly, via regexp match + reports runtime
//
var sm = require('service-metadata');

session.input.readAsJSON(function (error, num) { throwIf(error);
    var t0 = sm.timeElapsed;
    var iP = isPrime(num);
    var t1 = sm.timeElapsed;
    session.output.write(iP+" ("+(t1-t0)/1000.0+"s)");
});

function isPrime(n) {
    var re = /^.?$|^(..+?)\1+$/;
    return !re.test('1'.repeat(n));
}

function throwIf(error) { if (error)  throw error; } 

Reports
true (2.564s)
for smallest 17bit prime number 65537, and reports
true (424.544s)
for 100,000th prime number 1299709 (both on IDG hardware appliance).