Functional programming (correction) of a HTML + Javascript client calculator

Programming task Functional programming (correction) of a HTML + Javascript client calculator The following url contains an html page that shows the calculator we need - currently it is not functioning well [login to view URL] The task is to program a functionally working calculator with the following requirements: (Other functions are not required) Expectations Calculator should works with the control buttons in html (no direct keyboard entry) but the buttons have to pair hotkeys (eg. numeric keypad) The calculator design should be as provided by us (the customer) to the constructor (HTML layout should be followed) The programmer should directly program the calculator's functions into the provided design The calculator should be programmed so that the design can be easily changed later (eg. rearranging the buttons) without disturbing the operation The result of the calculation should be entered in a hidden input text (name = "num") field that will be transmitted using a POST method (recording format is MySql DOUBLE (10.3) type) The displayed result value should be programmed so that we are able to display in another number format eg. comma for decimal instead of point (this is a passable parameter in html "." Or ",") The result should be displayed with a spaced thousand separator - ".toLocaleString ('hu-HU')" example of displayed number format: 102 324,25 Calculator input buttons number buttons (0-9) add button (+) subtraction key "-" (with double function - see below) multiplication button "x" division button "÷" 1 character is deleted from the end of the song, the "<-" arrow key delete all "C" button ("clear all") decimal point "." equal button "=" Calculator Input Rules maximum input character length: 10 (DOUBLE (10.3) type number) disable entry of more than one zeros at the beginning of the number if first number is zero, it can be followed only by a decimal point duplicate zeros shouldn’t not be recorded at the beginning of the number number and operation keys should work on a mobile phone as well on a desktop PC, numpad keyboard should work for entry input and results up to 3 decimal places do not display the zeros at the end of a decimal entry of only one decimal point is allowed if decimal point is the first caracter, thenit should mean 0,... if there is already a minimum of 1 number recorded, the minus sign will mean sustraction if a negative operation key is the first character then a negative sign is added before the number and the additional operations are calculated with the negative number