What value types does JSON support, and what notable type is missing?

JSON has six value types — string, number, boolean, null, array, object — and crucially has no date type.

{
  "string": "hello",
  "number": 42,
  "float": 3.14,
  "boolean": true,
  "nothing": null,
  "array": [1, 2, 3],
  "object": { "nested": "value" }
}

A few rules matter in practice:

• Numbers carry no quotes — "plz": 1234, not "1234". Quoting a number turns it into a string, which is a common bug.
• Keys are always double-quoted strings — "name", never name or 'name' (this is where JSON differs from a JavaScript object literal, which allows bare keys).
• No comments — you cannot annotate a JSON document.

The big gotcha is dates. JSON has no date type, so a date like a birthday is stored as a plain string — e.g. "1.1.1980" or the ISO form "2024-01-15" — and your code must parse that string back into a real date object (in JavaScript, new Date(...)). Forgetting this and treating the string as a date is a classic source of bugs.

Tip: Prefer the ISO 8601 form ("2024-01-15T10:30:00Z") for dates in JSON — it's unambiguous and sorts correctly as text, unlike 1.1.1980.