Js calculator

Create a web based calculator which has the following:

Three HTML input fields:
- A number field (the first number in a calculation i.e. x)
- An operator select menu with standard calculator function as option elements (+-*/).
- A number field (the second number in a calculation i.e. y)
A submit button
When the submit button is clicked the calculation should be carried out in javascript
- A div with the id="answer", where the calculation is displayed.
- The contents of the answer div is replaced each time a calculation is made
- The x number field is changed to the calculated answer to allow for a duplicate calculation on the current result.
A CE button which clears all of the text fields and resets the answer to 0
- When clicked focus is returned to the x field. (Lookup .focus)

Abstract the logic for the calculation into it's own function
Add Square <option>
Add Square Root <option>
Add a ± button which inverts the current answer as well as the value in the x field
When an invalid number (such as a letter) is given, show an error message (styled in red) that their operation isn't possible.
Create a number pad or integer buttons, operators, and a . button to allow the user to click buttons to enter their numbers.
Use the onkeyup event listener to allow the user to put in the numbers and operator without needing to change between input fields (i.e. the "x" key selects the value x from the operators)

smurfik / calculator_js