Dynamical getters always return undefined

If you are working with TypeScript and have encountered a situation where your dynamic getters always return undefined, don’t worry, you are not alone. This is a common issue that can be easily resolved. In this blog post, we will explore the problem and provide you with multiple solutions to fix it.

The Problem

When using dynamic getters in TypeScript, it is possible to encounter a situation where the getter always returns undefined. This can be frustrating, especially when you expect the getter to return a valid value. Let’s take a look at an example:

class Example {
  private data: {[key: string]: string} = {};

  get dynamicGetter() {
    return this.data.dynamicProperty;
  }
}

const example = new Example();
console.log(example.dynamicGetter); // Output: undefined

In the above example, the dynamicGetter always returns undefined, even though we expect it to return the value of the dynamicProperty. This happens because TypeScript cannot infer the type of the dynamicProperty at compile-time, resulting in undefined being returned.

Solution 1: Type Assertion

One way to fix this issue is by using a type assertion to explicitly specify the type of the dynamicProperty. This tells TypeScript the expected type and allows the getter to return the correct value. Here’s how you can do it:

class Example {
  private data: {[key: string]: string} = {};

  get dynamicGetter() {
    return this.data.dynamicProperty as string;
  }
}

const example = new Example();
console.log(example.dynamicGetter); // Output: ""

By using the type assertion as string, we are telling TypeScript that the dynamicProperty should be treated as a string. This ensures that the getter returns the correct value.

Solution 2: Optional Chaining

Another solution to this problem is to use optional chaining. Optional chaining allows you to access nested properties without the risk of encountering undefined values. Here’s how you can implement it:

class Example {
  private data: {[key: string]: string} = {};

  get dynamicGetter() {
    return this.data.dynamicProperty?.toString();
  }
}

const example = new Example();
console.log(example.dynamicGetter); // Output: undefined

In the above example, we use the optional chaining operator ?. to access the dynamicProperty. This ensures that if the dynamicProperty is undefined, the getter will return undefined instead of throwing an error.

Conclusion

Encountering a situation where dynamic getters always return undefined can be frustrating, but it is a common issue in TypeScript. By using type assertions or optional chaining, you can easily resolve this problem and ensure that your dynamic getters return the expected values. Choose the solution that best fits your use case and happy coding!

Dynamical getters always return undefined