longestPrefix interview question solution

This is my attempt at solving the longestPrefix interview question from cassidoo's weekly newsletter.

Question:

Write a function to find the longest common prefix string in an array of strings.

Example:

$ longestPrefix(["cranberry","crawfish","crap"])
$ "cra"

$ longestPrefix(["parrot", "poodle", "fish"])
$ ""

Solution (try using browsing from a laptop if it doesn't load anything):

Comments and suggestions are welcome.