Write a JavaScript function on the following: a.) Create a function to extract a specified number of characters from a string. Function should accept a string input, start location and the number of characters to be extracted. Function should also validate if all parameters are of valid values such as non-empty string and valid integer values. b.) Create a function that will extract the first letter of every word in a sentence and place them in an array. Function should validate if the parameter value is a valid string