Objects

Instantiation

// in TS order of insertion is not guaranteed with objects (use Map for this)

// empty object
const obj1: { [key in string]: string } = {} // most common
const obj2: { [key: string]: string } = {}
const obj3: Record<string, string> = {}
const obj4: { [key in string]: string } = new Object()
const obj5: { [key in string]: string } = Object.create(null) // object without prototype

// pre-filled object
const obj6 = { key1: "value1", key2: "value2" } // most common
const obj7 = Object.fromEntries([["key1", "value1"], ["key2", "value2"]])

// using a separate interface
interface MyInterface {
  key1: string
  key2: string
}
const obj8: MyInterface = { key1: "value1", key2: "value2" }

// using a separate type
type MyType = {
  key1: string
  key2: string
}
const obj9: MyType = { key1: "value1", key2: "value2" }

// in Swift order of insertion is guaranteed with dictionaries

// use a dictionary when keys are dynamic
//   empty dictionary
let dict1: [String: String] = [:]
let dict2 = Dictionary<String, String>()
let dict3: Dictionary<String, String> = .init()

//   pre-filled dictionary
let dict4: [String: String] = ["key1": "value1", "key2": "value2"]
let dict5 = Dictionary(uniqueKeysWithValues: [("key1", "value1"), ("key2", "value2")])
let dict6 = Dictionary(uniqueKeysWithValues: zip(["key1", "key2"], ["value1", "value2"]))

// use a struct when keys are static
struct MyStruct {
  let key1: String
  let key2: String
}
let struct1 = MyStruct(key1: "value1", key2: "value2")

// use a named tuple when keys are static, useful as quick inline objects
let tuple1 = (key1: "value1", key2: "value2")

Accessing properties

const obj = { key1: "value1", key2: "value2" }
obj.key1 // "value1"
obj["key1"] // "value1"

// dictionaries
let dict = ["key1": "value1", "key2": "value2"]
dict["key1"] // "value1"

// structs
struct MyStruct {
  let key1: String
  let key2: String
}
let struct1 = MyStruct(key1: "value1", key2: "value2")
struct1.key1 // "value1"

// named tuples
let tuple1 = (key1: "value1", key2: "value2")
tuple1.key1 // "value1"
tuple1.0 // "value1"

keys, values, entries

Converting keys, values, entries to arrays

const keys = Object.keys(object)
// ["key1", "key2"]

const values = Object.values(object)
// ["value1", "value2"]

const entries = Object.entries(object)
// [["key1", "value1"], ["key2", "value2"]]

let keys = Array(dictionary.keys)
// ["key1", "key2"]

let values = Array(dictionary.values)
// ["value1", "value2"]

let entries = Array(dictionary)
// [("key1", "value1"), ("key2", "value2")]

Iterating over keys, values, entries

for (const key in object) {
  console.log("key: ", key)
}

for (const value of Object.values(object)) {
  console.log("value: ", value)
}

for (const [key, value] of Object.entries(object)) {
  console.log("entry: ", [key, value])
}

for key in dictionary.keys {
  print("key:", key)
}

for value in dictionary.values {
  print("value:", value)
}

for (key, value) in dictionary {
  print("entry:", (key, value))
}