TypeScript Empty Object Guide: Best Practices

What does an empty object mean in TypeScript?

Some think it’s a completely blank structure, while others see it as an unrestricted type. This small detail can confuse, leading to unexpected errors in code.

The way TypeScript handles empty objects depends on type rules, object literals, and assignable values. Understanding these concepts helps avoid mistakes and write safer code.

This blog breaks it all down with simple examples, showing how a TypeScript empty object behaves and when to use it.

What is an Empty Object in TypeScript?

In TypeScript, an empty object can be represented by {}. At first glance, it might seem like it refers to an object with no properties, but TypeScript treats {} as a wildcard object type that can hold any properties.

Example: Defining an Empty Object in TypeScript

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1const obj: {} = {}; // Valid: obj is an empty object
2const obj2: {} = { key: "value" }; // Also valid: {} allows any properties

Type Relationship of

Assignability of Empty Object

An empty object in TypeScript is assignable to all object types but is not assignable to primitive types such as string, number, or boolean.

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1const obj: {} = 42; // ❌ Error: Type 'number' is not assignable to type '{}'
2const obj2: {} = "text"; // ❌ Error: Type 'string' is not assignable to type '{}'
3const obj3: {} = true; // ❌ Error: Type 'boolean' is not assignable to type '{}'

Understanding the Empty Object Type in TypeScript

An empty object type ({}) is different from an empty object (const obj = {}). The former is a type definition, while the latter is an instance.

Key Characteristics of Empty Object Type

1. It is an object type with no explicitly defined properties.

2. It allows any object that does not contain primitive types.

3. It is different from Record<string, never>, which strictly prevents properties.

Example: Empty Object Type vs. Object with No Properties

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1type EmptyObjectType = {}; // Accepts any object
2const validObject: EmptyObjectType = { key: "value" }; // ✅ Allowed
3
4type StrictEmptyObject = Record<string, never>;
5const invalidObject: StrictEmptyObject = { key: "value" }; // ❌ Error: Property 'key' is not allowed

How Empty Objects Behave in Structural Typing

TypeScript follows structural typing, meaning that two object types are compatible if they have matching properties.

Example: Structural Typing with Empty Objects

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1type MyObject = {};
2const obj: MyObject = { name: "Alice", age: 30 }; // ✅ Allowed (structural typing)

Since {} does not define any properties, it is assignable to any object.

Handling Null and Undefined with Empty Objects

Empty Object and Type Null

By default, an empty object type {} does not allow null or undefined.

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1const obj: {} = null; // ❌ Error: Type 'null' is not assignable to type '{}'
2const obj2: {} = undefined; // ❌ Error: Type 'undefined' is not assignable to type '{}'

To allow these values, use a union type:

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1const obj: {} | null = null; // ✅ Allowed
2const obj2: {} | undefined = undefined; // ✅ Allowed

Using Empty Objects in Generic Functions

A generic function can use an empty object type as a type parameter to allow flexible usage.

Example: Generic Function with Empty Object Type

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1function processObject<T extends {}>(obj: T): T {
2  return obj;
3}
4
5const result = processObject({ name: "Alice" }); // ✅ Allowed
6const result2 = processObject(42); // ❌ Error: Type 'number' is not assignable to '{}'

Since T extends {} is used, only object types are assignable, excluding primitive types.

Extending Object in TypeScript

Why Use Extends Object?

Using T extends object ensures that a generic function only accepts valid objects.

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1function validate<T extends object>(data: T): void {
2  console.log(data);
3}
4
5validate({ name: "Alice" }); // ✅ Allowed
6validate("text"); // ❌ Error: Type 'string' is not assignable to 'object'

Common Errors When Working with Empty Objects

1. Assigning Primitive Types

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1const obj: {} = 123; // ❌ Error: Type 'number' is not assignable to type '{}'

2. Confusing with object

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1const obj: object = {}; // ✅ Allowed
2const obj2: {} = 42; // ❌ Error

• {} is stricter than object.

3. Using Undefined Values

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1const obj: {} = undefined; // ❌ Error: Type 'undefined' is not assignable to type '{}'

Best Practices for Working with Empty Objects

1. Use Record<string, never> when you want to prevent any properties.

2. Prefer T extends object over T extends {} in generic functions.

3. Avoid using {} unless explicitly required.

4. Ensure correct assignability to avoid unexpected errors.

Final Thoughts on TypeScript Empty Object

The TypeScript empty object may seem simple, but it has unique behaviors. It accepts any object but does not work with primitive values like strings or numbers. Using T extends object in generic functions helps maintain type safety and prevents mistakes. A clear understanding of these rules makes coding smoother and avoids unexpected errors.