J.S. What exactly does 'indexOf' and LastIndexOf' do?

Question

var str = "Please locate where 'locate' occurs!";
var pos = str.indexOf("locate");

Answer 1

1. string.indexOf(substr, pos);

It looks for the substr in string, starting from the given position pos, and returns the position where the match was found or -1 if nothing can be found.

For example:
let string = "Sololearn";
console.log(string.indexOf("Solo")); // 0, coz "Solo" was found at the begining
console.log(string.indexOf("solo")); // -1, not found, coz search is case-sensitive

The optional second parameter allows us to search starting from the given position

For example (let's find second occurrence of "ol"):
let string = "Sololearn";
console.log(string.indexOf("ol", 2)); // 3

You can find all occurrences with help of loop and this amazing method (will be task for you).

2. string.lastIndexOf(substr, pos);

This is a similar method that searches from the end of a string to its begining. It would list the occurrence in the reverse order.

For example:
let string = "Sololearn";
console.log(string.lastIndexOf("ol")); // 3

You can read more about this methods on MDN: https://developer.mozilla.org

Answer 2

Better try it on code playground, and tell us the output.

Answer 3

Index number 7 for the word staring pos of word "locate" . Count from index 0, the first letter from the left.

P l e a s e locate...
0 1 2 3 4 5 6 7

Answer 4

output = 7

I got it from w3school and it just didn't make sense: https://www.w3schools.com/js/tryit.asp?filename=tryjs_string_indexof