How can I implement constants in a TypeScript class?

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#1

How do I implement constants in a TypeScript class?

In TypeScript, using the const keyword to declare class properties results in an error: “A class member cannot have the ‘const’ keyword.” I want to clearly indicate that a property should not be modified, and I want the IDE or compiler to throw an error if an attempt is made to assign a new value to the property after it is declared.

Currently, I am using a read-only property like this:

get MY_CONSTANT(): number { return 10; }

But I am wondering if there is a better way to handle this in TypeScript to enforce constants in a class. Any suggestions for using TypeScript constants more effectively?

#2

Hello,

To enforce immutability in TypeScript, one of the most effective approaches is to use the readonly modifier on class properties. This ensures that a property can only be assigned a value once during initialization and prevents any further reassignment, making it behave like a constant.

Here’s how you can implement it:

class MyClass {
    readonly MY_CONSTANT: number = 10;
}

In the above example, MY_CONSTANT is declared with the readonly modifier. Once it is initialized with the value 10, it cannot be reassigned or modified later in the code. This guarantees that the value remains constant throughout the lifecycle of the object, effectively enforcing immutability for that property.

This approach is simple, easy to understand, and ensures that the property value is never changed accidentally, which is essential for maintaining the integrity of constant values in your application.

Thanks!

#3

Use get accessor for constants: Another option is to create a getter for your constant property. This approach allows you to define the constant as a computed value that can’t be changed once it’s assigned.

class MyClass { get MY_CONSTANT(): number { return 10; } }

By using a getter, you create a read-only property that doesn’t allow modifications while still giving the appearance of a constant.

#4

Hello Community,

If you are looking to create an immutable object constant in your code, using Object.freeze() is an excellent approach. This method can be applied to both arrays and plain objects to ensure they remain unmodifiable. It’s particularly useful when working with class properties and TypeScript constants that involve collections or complex data structures.

Here’s an example demonstrating how you can implement it:

class MyClass {
    readonly MY_CONSTANT = Object.freeze({ key: 'value' });
}

In this example, the Object.freeze() method is used to prevent any modifications to the object assigned to MY_CONSTANT. This ensures that once the object is defined, it remains immutable, and its properties cannot be altered. This is especially helpful when you want to guarantee the integrity of constant data, preventing accidental changes in your code.

By using Object.freeze(), you’re securing the object from any further modifications, which can be crucial for maintaining the stability of complex data structures or collections in your application.

Thank you