Are Letters in the Second String Present in the First?

Create a function that accepts an array of two strings and checks if the letters in the second string are present in the first string.

Examples

letterCheck(["trances", "nectar"]) ➞ true

letterCheck(["compadres", "DRAPES"]) ➞ true

letterCheck(["parses", "parsecs"]) ➞ false

Notes

• Function should not be case sensitive (as indicated in the second example).
• Both strings are presented as a single argument in the form of an array.
• Bonus: Solve this without RegEx.