// Groups
const imageDescription = 'This image has a resolution of 1440×900 pixels.';
const regexpSize = /([0-9]+)×([0-9]+)/;
const match = imageDescription.match(regexpSize);
console.log(`Width: ${match[1]} / Height: ${match[2]}.`);
// Expected output: "Width: 1440 / Height: 900."

// Backreferences
const findDuplicates = 'foo foo bar';
const regex = /\b(\w+)\s+\1\b/g;
console.log(findDuplicates.match(regex));
// Expected output: Array ["foo foo"]