title: Is it possible to do expressions/calculations in json?
body: <p>I am using the wonderful json-server as the backend of my application and it's really useful for hitting custom endpoints to retrieve some data. but what would be super useful if it allowed me to do calculations/expression so that i can mimic that backend behaviour too.</p>
  
  <p>take this data structure for example</p>
  
  <pre><code>{
    "products": [
      {
        "name": "football",
        "id": "SPO-001",
        "category": "sport",
        "price": 40,
        "couponApplied": "false",
        "coupons": [
          "daw124qdw",
          "a1212cxn"
        ]
      }
    ]
  }
  </code></pre>
  
  <p>I would like some way of saying something like <code>"discountPrice": couponApplied ? price * couponDiscount</code></p>
  
  <p>that's just me pseudo coding. but I would like to do something where I can calculate the price on the fly. or when I make a request it does a calculation and returns me the calculated data (like a backend app would)</p>
  
  <p>I understand I can make a request, apply the coupon and render that new price. or even make a post request and change the price. but that is all done client side. is there any way to do this either with json or json-server or any other solutions. if that makes sense?</p>