Contamination #1 -String-.js

An AI has infected a text with a character!!

This text is now fully mutated to this character.

If the text or the character are empty, return an empty string.
There will never be a case when both are empty as nothing is going on!!

Note: The character is a string of length 1 or an empty string.

Example
text before = "abc"
character   = "z"
text after  = "zzz"

contamination=(text,char)=>char.repeat(text.length)