Typescript JSON type

json.ts

/**
 * JSONValue is a type alias for narrowing or validating JSON.
 * Requires an indirection via the DelayedJsonValue interface
 * to establish a 'root' type, Record<string,JSONValue> causes
 * recursion errors.
 */
export type JSONValue =
  | JsonPrimitive
  | JsonArray
  | JsonObject
  | DelayedJsonValue;
type JsonPrimitive = string | number | boolean | null;
type JsonArray = Array<JSONValue>;
type JsonObject = {[key: string]: JSONValue};
interface DelayedJsonValue {
  value: JSONValue;
}

 // comprehensive JSON example
const myJson: JSONValue = {
  string: 'Hello, world!',
  number: 42,
  boolean: true,
  null: null,
  array: [
    'foo',
    123,
    false,
    null,
    {
      nestedString: 'bar',
      nestedNumber: 456,
      nestedBoolean: true,
      nestedNull: null,
      nestedArray: [],
    },
  ],
  object: {
    nestedString: 'baz',
    nestedNumber: 789,
    nestedBoolean: false,
    nestedNull: null,
    nestedArray: [
      'qux',
      987,
      true,
      null,
      {
        deeplyNestedString: 'quux',
        deeplyNestedNumber: 654,
        deeplyNestedBoolean: false,
        deeplyNestedNull: null,
        deeplyNestedArray: [],
      },
    ],
  },
};
isJsonValue(myJson); // true

export function isJsonValue(value: unknown): value is JSONValue {
  if (typeof value === 'string') {
    return true;
  }
  if (typeof value === 'number') {
    return true;
  }
  if (typeof value === 'boolean') {
    return true;
  }
  if (value === null) {
    return true;
  }
  if (Array.isArray(value)) {
    return value.every(isJsonValue);
  }
  if (typeof value === 'object') {
    return Object.values(value).every(isJsonValue);
  }
  return false;
}

export function assertIsJsonValue(value: unknown): asserts value is JSONValue {
  if (!isJsonValue(value)) {
    throw new Error('Value not valid JSON.');
  }
}