let str = 'Hello world, welcome to the JS Universe.';

console.log(str.indexOf('welcome')); // 13

console.log(str.indexOf('wall')); // -1

const fruits = ['Orange', 'Pineapple', 'Apple', 'Melon'];

console.log(fruits.indexOf('Melon')); // 3

console.log(fruits.indexOf('klkljkh')); // -1