Author: John Au-Yeung

Sometimes, we want to fix the error "TS2339: Property ‘x’ does not exist on type ‘Y’" with TypeScript.

In this article, we’ll look at how to fix the error "TS2339: Property ‘x’ does not exist on type ‘Y’" with TypeScript.

How to fix the error "TS2339: Property ‘x’ does not exist on type ‘Y’" with TypeScript?

To fix the error "TS2339: Property ‘x’ does not exist on type ‘Y’" with TypeScript, we should make sure the properties are listed in the interface that’s set as the type of the object.

For instance, we write

interface Images {
  main: string;
  [key: string]: string;
}

const getMainImageUrl = (images: Images): string => {
  return images.main;
};

to create the Images interface that has the main property.

Then we can access the images.main property in the getMainImageUrl function without TypeScript compiler errors.

Conclusion

To fix the error "TS2339: Property ‘x’ does not exist on type ‘Y’" with TypeScript, we should make sure the properties are listed in the interface that’s set as the type of the object.

Sometimes, we want to get properties of a class with TypeScript.

In this article, we’ll look at how to get properties of a class with TypeScript.

How to get properties of a class with TypeScript?

To get properties of a class with TypeScript, we can create an instance of it and then use Object.getOwnPropertyNames on the instance.

For instance, we write

class A {
  private a1 = "";
  public a2 = "";
}

const a = new A();
const array = Object.getOwnPropertyNames(a);

to create an A instance.

Then we call Object.getOwnPropertyNames with A instance a to get all the non-inherited properties’ names’ in the array.

Conclusion

To get properties of a class with TypeScript, we can create an instance of it and then use Object.getOwnPropertyNames on the instance.

Sometimes, we want to convert a set to an array in TypeScript.

In this article, we’ll look at how to convert a set to an array in TypeScript.

How to convert a set to an array in TypeScript?

To convert a set to an array in TypeScript, we can set the downlevelIteration option to true in tsconfig.json‘s compilerOptions.

Then we can use the spread operator to convert sets to arrays.

For instance, we write

{
  "compilerOptions": {
    "downlevelIteration": true
  }
}

to set the downlevelIteration option to true in our project.

Then we can use the spread operator on a set by writing

const arr = [...set];

to convert it to an array.

Conclusion

To convert a set to an array in TypeScript, we can set the downlevelIteration option to true in tsconfig.json‘s compilerOptions.

Then we can use the spread operator to convert sets to arrays.

Sometimes, we want to initialize an object in TypeScript.

In this article, we’ll look at how to initialize an object in TypeScript.

How to initialize an object in TypeScript?

To initialize an object in TypeScript, we can create an object that matches the properties and types specified in the interface.

For instance, we write

export interface Category {
  name: string;
  description: string;
}

const category: Category = {
  name: "My Category",
  description: "My Description",
};

to create the Category interface with the name and description string properties.

Then we create the category Category variable which has the same properties set to strings so that the properties and types matches the interface exactly.

We can also make the properties optional by putting ? after the property name, so we write

export interface Category {
  name?: string;
  description?: string;
}

to make name and description optional.

Conclusion

To initialize an object in TypeScript, we can create an object that matches the properties and types specified in the interface.

Sometimes, we want to add multiple type signatures for members or union types in TypeScript.

In this article, we’ll look at how to add multiple type signatures for members or union types in TypeScript.

How to add multiple type signatures for members or union types in TypeScript?

To add multiple type signatures for members or union types in TypeScript, we can add union types with TypeScript.

For instance, we write

interface Foo {
  bar: string | boolean;
}

to set the bar property to be either a string or boolean with string | boolean.

Conclusion

To add multiple type signatures for members or union types in TypeScript, we can add union types with TypeScript.