Explain the output?

Question

var str = "js css html php";
var res1 = str.substring(-2, 2);
var res2 = str.substr(-3, 3);
var res3 = str.slice(-3);
console.log(res1 + ""+ res2 + "" + res3);

Answer 1

This reference may help

https://www.w3schools.com/jsref/jsref_substring.asp
https://www.w3schools.com/jsref/jsref_substr.asp
https://www.w3schools.com/jsref/jsref_slice_string.asp

(Edited)