TypeScript: Define and Use Empty Object Type Correctly

While building a TypeScript function, you might want to accept an object as a parameter, but you don’t care what properties it has; you want to make sure it’s some object and not a string, number, or null.

For example, you are writing a logging function that accepts any object and prints it to the console. You don’t need to know the structure of the object, and you want to make sure it is not empty, like null or a primitive value like a number or string.

In such cases, you can use the empty object type {} to allow any object type, but still block primitives like 123, ‘text’, or null. In this tutorial, I will explain how to define and use an empty object type in TypeScript.

Table of Contents

Understanding the Empty Object Type in TypeScript

In TypeScript, an empty object type can be a bit tricky to define correctly. At first glance, you might think that using {} would create an empty object type. However, {} actually represents any non-nullish value, which means it can include objects with properties.

The Problem with {} in TypeScript

Using {} as an empty object type can lead to unexpected behavior. For instance, consider the following example:

function processObject(obj: {}) {
  // This function accepts any non-nullish value, not just empty objects
  console.log(obj);
}

processObject({ name: "John Doe" }); // Valid
processObject(42); // Valid
processObject(null); // Error

As you can see, the function processObject accepts any non-nullish value, including numbers and strings, which is not what we want when we aim to define an empty object type.

Check out: Difference Between Record vs Object in TypeScript

Defining a True Empty Object Type in TypeScript

To define a true empty object type, we can use Record<string, never>. This type represents an object with no properties, ensuring that only truly empty objects are allowed.

Using Record<string, never> in TypeScript

Here’s an example of how to use Record<string, never>:

function processEmptyObject(obj: Record<string, never>) {
  // This function accepts only empty objects
  console.log(obj);
}

processEmptyObject({}); // Valid
processEmptyObject({ name: "Jane Doe" }); // Error

In this example, processEmptyObject only accepts empty objects, and any attempt to pass an object with properties will result in a type error.

Define and Use an Empty Object Type in TypeScript

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Practical Use Cases for Empty Object Types in TypeScript

Empty object types {} are helpful when you want to accept or return any non-primitive object. They are often used in utility functions, default values, and generic types.

Initializing Empty Objects in TypeScript

One common use case for empty object types is initializing objects that will later be populated with data. For example, if you’re building a user management system for a company in New York, you might start with an empty user object and then add properties as needed:

interface User {
  name?: string;
  email?: string;
}

let user: User = {}; // Start with an empty object

// Later, add properties
user.name = "Alice Johnson";
user.email = "[email protected]";

Function Parameters in TypeScript

Another use case is defining function parameters that should start as empty objects. For instance, consider a configuration function for an application used by a tech startup in Silicon Valley:

interface Config {
  apiKey?: string;
  endpoint?: string;
}

function initializeConfig(config: Config = {}) {
  // Initialize with default values if not provided
  config.apiKey = config.apiKey || "default-api-key";
  config.endpoint = config.endpoint || "https://jsonplaceholder.typicode.com/posts/1";

  console.log("Initialized Config:", config);

  // Call the API
  fetch(config.endpoint, {
    method: "GET",
    headers: {
      "Content-Type": "application/json",
      "Authorization": `Bearer ${config.apiKey}`
    }
  })
    .then(response => response.json())
    .then(data => {
      console.log("API Response:", data);
    })
    .catch(error => {
      console.error("API Error:", error);
    });
}

// Call without custom config
initializeConfig();

// Call with custom config
initializeConfig({
  apiKey: "my-custom-key",
  endpoint: "https://jsonplaceholder.typicode.com/posts/2"
});

In this example, the initializeConfig function begins with an empty configuration object and populates it with default values as needed.

Check out: Search an Array of Objects by Property in TypeScript

Advanced Techniques with Empty Object Types in TypeScript

Empty object types {} may appear simple, but they behave differently in more complex scenarios. Let’s explore how to use them safely with functions, generics, and type checks.

Using Utility Types in TypeScript

TypeScript provides several utility types that can be combined with empty object types for more advanced use cases. One such utility type is Partial, which makes all properties of a type optional. This can be useful when working with objects that may start empty but will eventually have properties added:

interface Product {
  id: number;
  name: string;
  price: number;
}

let product: Partial<Product> = {}; // Start with an empty object
console.log("Initially:", product);

// Later, add properties
product.id = 101;
console.log("After setting id:", product);

product.name = "Laptop";
console.log("After setting name:", product);

product.price = 999.99;
console.log("After setting price:", product);

Check out: Convert an Object to an Array in TypeScript

Common Pitfalls and How to Avoid Them in TypeScript

Misunderstanding {} in TypeScript

As mentioned earlier, using {} can lead to unexpected behavior. Always prefer using Record<string, never> for defining truly empty object types.

Overusing Empty Object Types in TypeScript

While empty object types are useful, overusing them can lead to unclear code. Always consider whether an empty object type is the best choice for your specific use case. Sometimes, defining a more specific type with optional properties can be more appropriate.

Ignoring Type Inference in TypeScript

TypeScript’s type inference is powerful and can often determine the correct type without explicit annotations. Rely on type inference when possible to keep your code clean and maintainable.

Conclusion

Defining and using empty object types in TypeScript can be challenging, but with the right approach, you can avoid common pitfalls and leverage TypeScript’s powerful type system to create robust and maintainable code. Whether you’re initializing empty objects, defining function parameters, or combining utility types and conditional types, understanding how to work with empty object types will enhance your TypeScript skills and improve your code quality.

By following the techniques and best practices outlined in this tutorial, you’ll be well-equipped to handle empty object types in your own projects, whether you’re developing applications for clients in San Francisco, New York, or Silicon Valley.

Define and Use an Empty Object Type in TypeScript