RegExp.prototype.multiline

const regex1 = new RegExp("^football");
const regex2 = new RegExp("^football", "m");
console.log(regex1.multiline);
// Expected output: false
console.log(regex2.multiline);
// Expected output: true
console.log(regex1.test("rugby\nfootball"));
// Expected output: false
console.log(regex2.test("rugby\nfootball"));
// Expected output: true

const regex = /foo/m;
console.log(regex.multiline); // true