let timeRegex = /([0-9]{2}):([0-9]{2})/; console.log(timeRegex.exec("13:12")); // see [1] being 13 and [2] being 12 console.log(timeRegex.exec("10:10:10")); // this matches because we just said "should include pattern anywhere" timeRegex = /^([0-9]{2}):([0-9]{2})$/; console.log(timeRegex.exec("10:10:10")); // now it returns null console.log(timeRegex.exec("YOLO")); // also null