Create a simple "web-app" that we created using client-side HTML form, come up with our very own (custom-built) JS calculator.

One possible "look and feel" is shown below in attached screen-shot (CSS or style is not important. Functionality using JavaScript is major part of the current focus)

When first loaded, both input (type=number) fields are empty and when user clicks any of the numeric buttons, the "Operand 1" should be populated.
[Above is one possible visual after pressing "1","2","3" & "+" buttons in sequence. Notice the "operation" buttons are disabled on pressing any one of them (+ in this case).]

When the user presses any operation (ie /, x, +, -) the "focus" should shift to "Operand 2" and the numeric buttons should now start populating that second input box.

[Above is one possible visual after further pressing "4","5","6" in sequence]

[Above is one possible visual after pressing the "=" button]

The "clear" button should reset everything (ie remove all entries from Operand 1 & 2 as well as enable all "operation" buttons and bring the "focus" back to first input box.)
 
 

1 4 7 250 2 3 1 6 X 8 9 Clear 0 =