Awesome

RegExp.prototype.flags 

An ES6 spec-compliant RegExp.prototype.flags shim. Invoke its "shim" method to shim RegExp.prototype.flags if it is unavailable. Note: RegExp#flags requires a true ES5 environment - specifically, one with ES5 getters.

This package implements the es-shim API interface. It works in an ES5-supported environment and complies with the spec.

Most common usage:

var flags = require('regexp.prototype.flags');
var assert = require('assert');

assert(flags(/a/) === '');
assert(flags(new RegExp('a')) === '');
assert(flags(/a/mig) === 'gim');
assert(flags(new RegExp('a', 'mig')) === 'gim');

if (!RegExp.prototype.flags) {
	flags.shim();
}

assert(flags(/a/) === /a/.flags);
assert(flags(new RegExp('a')) === new RegExp('a').flags);
assert(flags(/a/mig) === /a/mig.flags);
assert(flags(new RegExp('a', 'mig')) === new RegExp('a', 'mig').flags);

Tests

Simply clone the repo, npm install, and run npm test