Create a function named calcExpression(). The purpose of this function is to append the calculated value to the expression displayed on the calculator screen. The function has no parameters. Add the following commands: a. Declare a variable named cString that is equal to the text contained in the calcwindow field of the calculator form. b. Use the eval() method to store the numeric value of cString in a variable named cValue. c. Change the text string value of the calcwindow field from the calculator form to cString = cValue where cString is the value of the cString variable and cValue is the value of the cValue variable.