What is JavaScript indexOf()?

So what is indexOf()?

indexOf() finds the first occurrence of a string and returns the index. So an example:


let example = 'Hello World';
console.log(example.indexOf('e'));

// 1

The above should return 1. Because the letter 'e' in the string is at index 1.

But if the indexOf() string does not exist like example:


let example = 'Hello World';
console.log(example.indexOf('t'));

// -1

It will return -1 if it does not exist.

It will always return the first occurrence even if the indexOf() string is not a letter but a word.


let example = 'Hello World';
console.log(example.indexOf('ello');

// 1