While building an e-commerce application in TypeScript, you might define a ProductCategory enum for valid categories like ‘electronics’, ‘clothing’, and ‘food’. When receiving data from a user or an API, it’s important to check if the provided category actually exists in the enum.
This prevents invalid values from being processed or stored. This ensures your application handles only valid, expected data and avoids potential bugs.
In this tutorial, I will explain how to check if a value exists in an Enum in TypeScript. Enums allow developers to define a set of named constants, making it easier to document intent and create distinct cases.
Enums are a powerful feature in TypeScript that can help improve code readability and maintainability. We’ll explore different methods to determine if a specific value is part of an enum and provide real-world examples to illustrate the concepts.
Understand Enums in TypeScript
Before diving into checking if a value exists in an enum, let’s briefly review what enums are in TypeScript. An enum is a way to define a set of named constants. Each constant in the enum is assigned a numeric value, starting from 0 by default.
Here’s an example of a simple enum representing different states in the United States:
enum USState {
California,
Texas,
Florida,
NewYork,
Illinois
}Check out: Convert TypeScript Enum to String
Check if a Value Exists in an Enum in TypeScript
Now, let’s explore different ways to check if a value exists in an enum in TypeScript.
Method 1: Using the in Operator in TypeScript
One straightforward approach to check if a value exists in an enum is by using the in operator. The in operator checks if a property exists in an object or its prototype chain. You can use the in operator to check if a value is a property of the enum object.
Here’s an example:
enum USState {
California,
Texas,
Florida,
NewYork,
Illinois
}
const state = 'California';
if (state in USState) {
console.log(`${state} is a valid US state.`);
} else {
console.log(`${state} is not a valid US state.`);
}In this code, we define the USState enum and then check if the state variable exists as a property in the USState enum using the in operator. If the value exists, it means it is a valid enum value.
Check out: Convert TypeScript Enums to Arrays
Method 2: Using the Enum Object in TypeScript
Another approach to check if a value exists in an enum is by directly accessing the enum object. Enums in TypeScript are essentially objects, so you can use bracket notation or dot notation to access the enum values.
Here’s an example using bracket notation:
enum USState {
California,
Texas,
Florida,
NewYork,
Illinois
}
const state = 'Texas';
if (USState[state] !== undefined) {
console.log(`${state} is a valid US state.`);
} else {
console.log(`${state} is not a valid US state.`);
}This code uses bracket notation USState[state] to access the enum value. If the value exists in the enum, it will return the corresponding numeric value.
If the value doesn’t exist, it will return undefined. We can check for its presence by comparing it with undefined.
Method 3: Using the hasOwnProperty Method in TypeScript
Another way to check if a value exists in an enum is by using the hasOwnProperty method. This method is available on all JavaScript objects and returns a boolean indicating whether the object has the specified property as its own property.
Here’s an example:
enum USState {
California,
Texas,
Florida,
NewYork,
Illinois
}
const state = 'Florida';
if (USState.hasOwnProperty(state)) {
console.log(`${state} is a valid US state.`);
} else {
console.log(`${state} is not a valid US state.`);
}In this code, we use the hasOwnProperty method on the USState enum object to check if the state value exists as a property. If it does, it will return true, indicating that it is a valid enum value.
Check out: Check String in Enum TypeScript
Real-World Example in TypeScript
Let’s consider a real-world scenario where checking if a value exists in an enum can be useful. Imagine you are building an e-commerce application that allows users to select their shipping state. You want to ensure that the user selects a valid US state from a predefined list.
Here’s an example of how you can use enums and check if the selected state is valid:
// Define the enum
enum USState {
California = 'CA',
Texas = 'TX',
Florida = 'FL',
NewYork = 'NY',
Illinois = 'IL'
}
// Function to process the order based on state code
function processOrder(stateCode: string) {
// Find the enum entry that matches the state code
const stateEntry = Object.entries(USState).find(([_, code]) => code === stateCode);
if (stateEntry) {
const [stateName, code] = stateEntry;
console.log(`Processing order for ${stateName}`);
// Add your order processing logic here
} else {
console.log('Invalid shipping state selected.');
// Handle invalid state code here
}
}
// Example usage
processOrder('CA'); // Output: Processing order for California
processOrder('TX'); // Output: Processing order for Texas
processOrder('NY'); // Output: Processing order for NewYork
processOrder('GA'); // Output: Invalid shipping state selected.
This example defines the USState enum with state abbreviations as values. The processOrder function takes the selected state as a parameter and checks if it exists in the USState enum using the in operator.
If the state is valid, it proceeds with the order processing logic. If the state is invalid, it handles the case accordingly.
Conclusion
Checking if a value exists in an enum is a common task in TypeScript development. In this tutorial, we explored different methods to achieve this, including using the in operator, accessing the enum object directly, and using the hasOwnProperty method. By understanding these techniques, you can ensure that your code handles enum values correctly and provides a better user experience.
Remember, enums are a powerful feature in TypeScript that can help improve code readability and maintainability. When working with enums, it is important to validate user input and handle cases where invalid values may be provided.
I hope this tutorial has helped you understand how to check if a value exists in an enum in TypeScript. Happy coding!
You may like to read:
- Enums vs String Literal Unions in TypeScript
- Convert TypeScript Enum to String
- Use TypeScript Enums in Classes
- Use TypeScript Enums as Object Keys
I am Bijay Kumar, a Microsoft MVP in SharePoint. Apart from SharePoint, I started working on Python, Machine learning, and artificial intelligence for the last 5 years. During this time I got expertise in various Python libraries also like Tkinter, Pandas, NumPy, Turtle, Django, Matplotlib, Tensorflow, Scipy, Scikit-Learn, etc… for various clients in the United States, Canada, the United Kingdom, Australia, New Zealand, etc. Check out my profile.
