Calculator

First goal: entering digits, addition, equals sign

Backlog:

starting new calculation after equals sign
continue calculation after equals sign
subtraction
unary - operator
multiplication
division
Pressing two operation signs after one another?
Handling overflow
saving & loading calculator
Concurrent usage

First goal: entering digits, addition, equals sign

Scenario:

{0} 35 + 4 = {39}

API design

Starting a new calculator

/calculator PUT
{
}

Response:

{
    id: "id945"
}

Pressing a button

/calculator?id=1342345 PUT
{
    buttonPressed: "5"
}

Response:

{
  id: "id945",
  display: "5"
}