正则的预查

const res=/ES(?=2015|2016)/
console.log(res.exec('ES2015'));
console.log(res.exec('ES2016'));
console.log(res.exec('ES2017'));

const res=/ES(?!2015|2016)/
console.log(res.exec('ES2015'));
console.log(res.exec('ES2016'));
console.log(res.exec('ES2017'));

const res=/(?<=2015|2016)E/
console.log(res.exec('2015ES'));
console.log(res.exec('2016ES'));
console.log(res.exec('2017ES'));