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Converting PascalCase to CamelCase in JavaScript Records Using TypeScript

Updated: at 02:12 PM

Converting PascalCase to CamelCase in TypeScript: A Type-Safe Approach with CatList

🚨 Critical Warning (Updated on September 7th, 2023): Although the code examples and methodologies discussed in this blog post are technically correct, they exhibit serious shortcomings when deployed in real-world applications. For an in-depth look at these deficiencies, and how to address them, please read this urgent follow-up post.

One of the advantages of TypeScript is type safety, which helps ensure your data behaves as you expect. A task that can come up fairly often is the conversion of object keys from PascalCase to camelCase. In this blog post, we’ll explore how to accomplish this transformation while leveraging TypeScript’s type-safe capabilities, specifically through the Record type and Object.entries() function.

Record Type in TypeScript: An Asset for Type Safety

The Record type is an invaluable tool for creating type-safe objects in TypeScript. Consider the following line:

let camelCaseCats: Record<string, typeof cat[keyof typeof cat]> = {};

With Record<K, T>, we can dictate that the keys (K) will be strings and the values (T) will hold the same type as those in our cat object. This is TypeScript’s built-in mechanism for guaranteeing that both the keys and values conform to the expected types.

Unlocking Object Iteration with Object.entries()

The function Object.entries() is native to JavaScript and also usable in TypeScript. It takes an object and returns an array containing its own enumerable property [key, value] pairs, making object iteration a breeze.

for (const [key, value] of Object.entries(cat)) {
  // Perform operations here

A Complete Example: Converting CatList Array to CamelCase

Let’s assume we have an array called catList, each element of which is an object of type Cats. The keys in these Cats objects are in PascalCase, and we aim to convert them to camelCase.

Here’s our type and sample data:

type Cats = {
  CatName: string;
  IsHungry: boolean;
  LastFedDate: string | null;

const catList: Cats[] = [
    CatName: "Whiskers",
    IsHungry: true,
    LastFedDate: "2023-09-01"
    CatName: "Fluffy",
    IsHungry: false,
    LastFedDate: null

To perform the conversion while maintaining type safety through the Record type, we can do:

function convertToCamelCase(str: string): string {
  return str.charAt(0).toLowerCase() + str.slice(1);

const camelCasedCats = => {
  let camelCaseCats: Record<string, typeof cat[keyof typeof cat]> = {};
  for (const [key, value] of Object.entries(cat)) {
    camelCaseCats[convertToCamelCase(key)] = value === null ? 'unassigned' : value;
  return camelCaseCats;


Upon executing this code, camelCasedCats will become an array of objects with camelCased keys. TypeScript’s type safety will be maintained thanks to the Record type.

Generalizing This Approach

After implementing this logic specifically for our catList array, you might be wondering how to make this solution more generalized. Indeed, creating a reusable function to convert PascalCase to camelCase can be beneficial for various scenarios. So, let’s see how we can build a generic utility function for this task.

Convertible: A Generic Type

The first step is to define a generic type that describes the objects we’ll be converting. In TypeScript, this could be designed like so:

type Convertible<T> = Record<string, typeof T[keyof T]>;

Here, Convertible<T> serves as a blueprint for any object that has string keys and values of some type T.

Utility Function: mapToCamelCaseObject

Next, we craft a utility function that utilizes this generic type:

export const mapToCamelCaseObject = <T>(inputObject: Convertible<T>): Convertible<T> => {
  let camelCaseResult: Convertible<T> = {};
  const convertToCamelCase = (input: string): string => 
    input.length === 0 ? '' : input.charAt(0).toLowerCase() + input.slice(1);

  for (const [key, value] of Object.entries(inputObject)) {
    camelCaseResult[convertToCamelCase(key)] = value === null ? 'unassigned' : value;
  return camelCaseResult;

In this function, inputObject is of type Convertible<T>, making the function applicable to a variety of object types. The conversion logic is the same as before, but now it’s packaged into a reusable function.

Sample Usage

Using this utility function is straightforward. Let’s say you have an array of objects in PascalCase (e.g., catList), you could convert it to camelCase like so:

// Assuming catList is already defined
const camelCaseCats =;

By generalizing this approach, we’ve made it easy to apply PascalCase to camelCase conversion across different types of data structures. This keeps your code DRY (Don’t Repeat Yourself) and makes it more maintainable and scalable.


We’ve seen how the task of converting object keys from PascalCase to camelCase can be performed in a type-safe manner using TypeScript. By leveraging the Record type, we ensure that our keys and values conform to the data types we expect, mitigating potential errors down the line. Coupled with Object.entries(), which facilitates straightforward iteration over object properties, we can accomplish this task with both efficiency and safety.

Understanding these features can go a long way in making your TypeScript code not just functional but also robust. After all, one of the significant benefits of using TypeScript is its type-safe nature, which helps catch potential issues before they turn into runtime errors. Happy coding!

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