Working with JSON in Scala.js

Zakaria AmineMay 9th, 2018Last Updated: May 9th, 2018

0 67 2 minutes read

Introduction

Working with JSON is almost inevitable regardless of the environment. In this post, we will go through different ways of serializing/deserializing (or encoding/decoding as some may call it) objects from/to JSON in Scala.js. As of the date this post is written, there are three main tools that convert objects to/from JSON:

uPickle
Circe
scalajs-dom (using JSON.stringify() and parse())

We will use the following object for all the examples for uPickle and Circe:

case class Car(id: String, brand: String, model: String) {}

using scalajs-dom requires a slight modification to the object as only js.Object is allowed

class Car extends js.Object {
  var id: String = _
  var brand: String = _
  var model: String = _
}

Serializing

uPickle:

Using uPickle, it is enough to create an object that configures the types to be read/written :

import upickle.default.{ReadWriter => RW, macroRW}

object Car{
  implicit def rw: RW[Car] = macroRW
}

and then:

val mercedes = new Car("1", "Mercedes", "2015")
    
    val mercedesJSON = write[Car](mercedes)

     println(mercedesJSON)

     //result: {"id":"1","brand":"Mercedes","model":"2015"}

Circe:

Circe requires the configuration of encoders/decoders:

import io.circe.{Decoder, Encoder}
import io.circe.generic.semiauto._

object Expense {
  implicit val carDecoder: Decoder[Car] = deriveDecoder
  implicit val carEncoder: Encoder[Car] = deriveEncoder
}

and then:

import io.circe.syntax._

    val mercedes = new Car("1", "Mercedes", "2015")

    val mercedesJSON = mercedes.asJson

    println(mercedes.asJson)
     
     //result is indented by default &#55357;&#56898; for making the output oneline : .asJson.noSpaces
     /*  {
      "id": "1",
      "brand": "Mercedes",
      "model": "2015"
      }
      */

scalajs-dom:

using scalajs-dom requires the addition of scalacOptions += "-P:scalajs:sjsDefinedByDefault" to the build file, since @ScalaJSDefined is meant to be deprecated.

and then :

val mercedes = new Car()
    mercedes.id = "10"
    mercedes.model = "1980"
    mercedes.brand = "Mercedes"
    println(JSON.stringify(mercedes))

    //result: {"id":"10","brand":"Mercedes","model":"1980"}

Deserializing

uPickle:

val mercedesJSON = """{"id":"10","brand":"Mercedes","model":"1980"}"""
    val mercedes = read[Car](mercedesJSON)
    println(mercedes.id)
    // 10
    println(mercedes.model)
    //  1980
    println(mercedes.brand)
    // Mercedes

Circe:

val mercedesJSON = """{"id":"10","brand":"Mercedes","model":"1980"}"""
    val mercedes = decode[Car](mercedesJSON).toTry.get
    println(mercedes.id)
    // 10
    println(mercedes.model)
    //  1980
    println(mercedes.brand)
    // Mercedes

scalajs-dom:

val mercedesJSON = """{"id":"10","brand":"Mercedes","model":"1980"}"""
    val mercedes = JSON.parse(mercedesJSON).asInstanceOf[Car]
    println(mercedes.id)
    // 10
    println(mercedes.model)
    //  1980
    println(mercedes.brand)
    // Mercedes

Wrap up

We have walked through different libraries that allow serializing/deserializing JSON in Scala.Js. All the methods work in pretty much the same way, so there is no preferred way. The choice is left to the developer.

Published on Web Code Geeks with permission by Zakaria Amine, partner at our WCG program. See the original article here: Working with JSON in Scala.js

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