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Access JSON properties dynamically like JavaScript

Access JSON properties dynamically like JavaScript


Access JSON properties dynamically like JavaScript using Swift 4.2's new @dynamicMemberLookup feature.

DynamicJSON is a dynamically typed parser for JSON built upon the new @dynamicMemberLookup feature introduced by Chris Lattner in Swift 4.2. This allows us to access arbitrary object members which are resolved at runtime, allowing Swift to be as flexible as JavaScript when it comes to JSON.


if let jsonObject = try? JSONSerialization.jsonObject(with: data, options: []) as? [String: Any],
   let user = jsonObject["user"] as? [String: Any],
   let username = user["username"] as? String {
	// ...


let username = JSON(data).user?.username?.string


pod 'DynamicJSON'
github "saoudrizwan/DynamicJSON"
  • Or drag and drop DynamicJSON.swift into your project.

And import DynamicJSON in the files you'd like to use it.


1. Initialize 🐣

Throw Anything into a JSON object to get started

let json = JSON(Data())
           JSON(["key": "value"])
           JSON(["element", 1])
           JSON("Hello world")

...or cast a literal as JSON

let json = "Hello world" as JSON
           123 as JSON
           [1, 2, 3] as JSON

let user: JSON = [
	"username": "Saoud",
	"age": 21,
	"address": [
	    "zip": "12345",
	    "city": "San Diego"

2. Drill in ⛏

Treat JSON objects like you're in JavaScript Land

let dictionary = json.dictionary
let array = json[0]?.cars?.array
let string = json[3]?.users?[1]?.username?.string
let nsnumber = json.creditCard?.pin?.number
let double = json[3]?[1]?.height?.double
let int = json[0]?.age.int
let bool = json.biography?.isHuman?.bool

Note how JSON doesn't actually have properties like cars or users, instead it uses dynamic member lookup to traverse through its associated JSON data to find the object you're looking for.

In case you have a key that's an actual property of JSON, like number or description for example, just use the string subscript accessor like so:

let number = json.account?.contact?["number"]?.number
let description = json.user?.biography?["description"]?.string

3. Have fun 🤪

JSON conforms to Comparable

let json1 = JSON(jsonData1)
let json2 = JSON(jsonData2)

// Equality applies to all types (Dictionary, Array, String, NSNumber, Bool, NSNull)
let isEqual = json1 == json2

// Less/greater than only applies to NSNumbers (Double, Int) and Strings
let isLessThan = json1 < json2
let isLessThanOrEqual = json1 <= json2
let isGreaterThan = json1 > json2
let isGreaterThanOrEqual = json1 >= json2

Pretty print for debug purposes


Convert to raw object

let anyObject = json.object

Convert to Data

let data = json.data() // optionally specify options...