// indexOf(): Takes takes a substring and if the substring exists in a string it returns the first position of the substring if does not exist it returns -1

string.indexOf(substring)

let string = '30 Days Of JavaScript'

console.log(string.indexOf('D')) // 3

console.log(string.indexOf('Days')) // 3

console.log(string.indexOf('days')) // -1

console.log(string.indexOf('a')) // 4

console.log(string.indexOf('JavaScript')) // 11

console.log(string.indexOf('Script')) //15

console.log(string.indexOf('script')) // -1