how to get the index of the element in js code example

Example 1: indexof javascript

arr.indexOf(searchElement[, fromIndex])

Example 2: js index to index

let array = [5, "Foo", 3, "Bar"];
array.slice(2);
// Output = [3, "Bar"]

let string = "Volvo Cars";
string.slice(2);
// Output = "lvo cars"