Update index-of.en.md

Add clarification
4 years ago · 07b7a7b7cd
1 changed files with 1 additions and 0 deletions
--- a/subjects/index-of.en.md
+++ b/subjects/index-of.en.md
@ -9,6 +9,7 @@ Create 3 functions:

 > If a value is not found, the returned index is -1

+> functions should have array element as first argument
 > `indexOf` and `lastIndexOf` takes an additionnal `fromIndex` argument
 > that allow you to begin searching from a specific index.