JSON types

Let’s put our knowledge to the test, by defining a type that describes any allowable JSON value.

Here’s the relevant section of the specification:

md
A JSON value MUST be an
- object
- array
- number
- string,
or one of the following three literal names:
- false
- true
- null

Here’s your starting point code:

ts
type JSONObject = any
type JSONArray = any
type JSONValue = any
 
////// DO NOT EDIT ANY CODE BELOW THIS LINE //////
function isJSON(arg: JSONValue) {}
 
// POSITIVE test cases (must pass)
isJSON("hello")
isJSON([4, 8, 15, 16, 23, 42])
isJSON({ greeting: "hello" })
isJSON(false)
isJSON(true)
isJSON(null)
isJSON({ a: { b: [2, 3, "foo"] } })
 
// NEGATIVE test cases (must fail)
// @ts-expect-error
Unused '@ts-expect-error' directive.2578Unused '@ts-expect-error' directive.
isJSON(() => "")
// @ts-expect-error
Unused '@ts-expect-error' directive.2578Unused '@ts-expect-error' directive.
isJSON(class {})
// @ts-expect-error
Unused '@ts-expect-error' directive.2578Unused '@ts-expect-error' directive.
isJSON(undefined)
// @ts-expect-error
isJSON(BigInt(143))
// @ts-expect-error
Unused '@ts-expect-error' directive.2578Unused '@ts-expect-error' directive.
isJSON(isJSON)Try

ts
type JSONPrimitive = string | number | boolean | null
type JSONObject = { [k: string]: JSONValue }
type JSONArray = JSONValue[]
type JSONValue = JSONArray | JSONObject | JSONPrimitive
 
////// DO NOT EDIT ANY CODE BELOW THIS LINE //////
function isJSON(arg: JSONValue) {}
 
// POSITIVE test cases (must pass)
isJSON("hello")
isJSON([4, 8, 15, 16, 23, 42])
isJSON({ greeting: "hello" })
isJSON(false)
isJSON(true)
isJSON(null)
isJSON({ a: { b: [2, 3, "foo"] } })
 
// NEGATIVE test cases (must fail)
// @ts-expect-error
isJSON(() => "")
// @ts-expect-error
isJSON(class {})
// @ts-expect-error
isJSON(undefined)
// @ts-expect-error
isJSON(BigInt(143))
// @ts-expect-error
isJSON(isJSON)Try