const string = 'Hello hello hello';
// performing a replacement
const result1 = string.replace(/hello/, 'world');
console.log(result1); // Hello world hello
// performing global replacement
const result2 = string.replace(/hello/g, 'world');
console.log(result2); // Hello world world
// performing case-insensitive replacement
const result3 = string.replace(/hello/i, 'world');
console.log(result3); // world hello hello
// performing global case-insensitive replacement
const result4 = string.replace(/hello/gi, 'world');
console.log(result4); // world world world