JS with Types Start

Type expression

object, Object and {}

  • Basics
  • Tested with TypeScript 5.9

Three similar spellings mean different things. object (lowercase) accepts any value that is not a primitive: objects, arrays, functions. Object (capitalized) and the empty type {} accept every value except null and undefined, numbers and strings included.

None of them says what properties the value has, so reading item.sku from an object is an error (TS2339). When you know the shape, write it: {{ sku: string, price: number }}, or a @typedef.

At a glance

Use JSDoc in a .js file TypeScript in a .ts file
Any non-primitive /** @type {object} */ : object
Almost anything /** @type {Object} */ or /** @type {{}} */ : Object or : {}
A specific shape /** @type {{ sku: string }} */ : { sku: string }

Examples

options.js Error confirmed 5.9.3 TypeScript 5.9.3, run 21 October 2026: options.js(9,11): error TS2345: Argument of type 'number' is not assignable to parameter of type 'object'. 6.0.3 TypeScript 6.0.3, run 21 October 2026: the same as 5.9.3. options.js(9,11): error TS2345: Argument of type 'number' is not assignable to parameter of type 'object'. 7.0.2 TypeScript 7.0.2, run 21 October 2026: the same as 5.9.3. options.js(9,11): error TS2345: Argument of type 'number' is not assignable to parameter of type 'object'. checked 21 October 2026 
/** @param {object} options */
export function configure(options) {
  return Object.keys(options).length;
}

configure({ theme: "dark" });
configure([1, 2]);
configure(42);error TS2345: Argument of type 'number' is not assignable to parameter of type 'object'.
object accepts any non-primitive value.
jsconfig.json for this example 
{
  "compilerOptions": {
    "checkJs": true,
    "noEmit": true,
    "strict": true,
    "target": "es2022",
    "module": "nodenext",
    "types": []
  },
  "include": ["*.js"]
}
item.js Error confirmed 5.9.3 TypeScript 5.9.3, run 21 October 2026: item.js(4,15): error TS2339: Property 'sku' does not exist on type 'object'. 6.0.3 TypeScript 6.0.3, run 21 October 2026: the same as 5.9.3. item.js(4,15): error TS2339: Property 'sku' does not exist on type 'object'. 7.0.2 TypeScript 7.0.2, run 21 October 2026: the same as 5.9.3. item.js(4,15): error TS2339: Property 'sku' does not exist on type 'object'. checked 21 October 2026 
/** @param {object} item */
export function skuOf(item) {
  return item.sku;error TS2339: Property 'sku' does not exist on type 'object'.
}
object says nothing about properties.
jsconfig.json for this example 
{
  "compilerOptions": {
    "checkJs": true,
    "noEmit": true,
    "strict": true,
    "target": "es2022",
    "module": "nodenext",
    "types": []
  },
  "include": ["*.js"]
}
loose.js TypeScript 5.9.3 TypeScript 5.9.3, run 21 October 2026: No errors. 6.0.3 TypeScript 6.0.3, run 21 October 2026: the same as 5.9.3. No errors. 7.0.2 TypeScript 7.0.2, run 21 October 2026: the same as 5.9.3. No errors. checked 21 October 2026 
/** @type {Object} */
let a = 42;

/** @type {{}} */
let b = "text";

// Both accept primitives; only null and undefined are rejected.
a = true;
b = 0;

export { a, b };
Object and {} accept almost anything.
jsconfig.json for this example 
{
  "compilerOptions": {
    "checkJs": true,
    "noEmit": true,
    "strict": true,
    "target": "es2022",
    "module": "nodenext",
    "types": []
  },
  "include": ["*.js"]
}

Which one to write

Write object for "some object, I only pass it along" (a cache key, an options bag you forward unchanged). Write the shape when you read properties from it. Avoid Object and {}: they look like "an object" but accept 42 and "text", as the third example shows.

In @typedef {object} Name followed by @property lines, object (or Object) is part of the tag syntax: it starts an object type whose properties the following lines describe.

Without noImplicitAny

The handbook notes that with noImplicitAny off, TypeScript reads Object and object in JSDoc as any. With strict, which turns noImplicitAny on, they keep the meanings above, which is what every example on this site uses.

Gotchas

  • Arrays and functions are objects: configure([1, 2]) passes an object parameter.
  • For a dictionary with string keys, write Record<string, T> rather than object.

Questions

What is the difference between object and Object in JSDoc?

With strict, object accepts only non-primitive values, while Object accepts any value except null and undefined. Neither lists properties.

  • Type expression

    Object shapes

    Writing an object type inline in JSDoc: double braces, optional properties with ?, commas or semicolons, and the postfix = that does not mean optional.

  • Type expression

    Record<K, V> and Object.<K, V>

    Record<K, V> types an object used as a dictionary. In JSDoc it is written as in TypeScript; Object.<K, V> and index signatures mean the same thing.

  • Type expression

    Primitive types

    The primitive types in JSDoc are string, number, boolean, bigint and symbol, written in lowercase as in TypeScript. Examples, and the capital-letter trap.

  • JSDoc tag

    @typedef

    The JSDoc @typedef tag names a reusable type: an object type built from @property lines, a union or anything else. Every @typedef in a module is exported.

Sources

Last reviewed 20 October 2026.