Lynn «Кофеман»

const array = [ 0, 0, 1, 1, 2, 2, 3, 3, 4, 4 ];
const arrUniq = [ ...new Set(array) ]; // [ 0, 1, 2, 3, 4 ]

crypto.createHash('sha1').update(str).digest('latin1'); // raw_output
crypto.createHash('sha1').update(str).digest('base64'); // сразу base64

async function sha1(str) {
    const buf = Uint8Array.from(unescape(encodeURIComponent(str)), c=>c.charCodeAt(0)).buffer;
    const digest = await crypto.subtle.digest('SHA-1', buf);
    const raw = String.fromCharCode.apply(null, new Uint8Array(digest));
    return raw; // 20-символьная строка
    // или
    return btoa(raw); // base64
}

const findUnique = (l) => l.reduce((a, b) => a ^ b);

return str.replace(/^(\d{4})(\d+)(\d{4})$/, (m, p1, p2, p3) => p1 + '*'.repeat(p2.length) + p3);

The third argument can be used to create virtual mocks – mocks of modules that don't exist anywhere in the system:

jest.mock(
  '../moduleName',
  () => {
    /*
     * Custom implementation of a module that doesn't exist in JS,
     * like a generated module or a native module in react-native.
     */
  },
  {virtual: true},
);