Category: TypeScript

Sometimes, we want to specify the return type in a TypeScript arrow function.

In this article, we’ll look at how to specify the return type in a TypeScript arrow function.

How to specify the return type in a TypeScript arrow function?

To specify the return type in a TypeScript arrow function, we put a colon and the type after between the signature and the arrow.

For instance, we write

const addTodo = (text: string): AddTodoAction => ({
  type: "ADD_TODO",
  text: text,
});

to make the addTodo function return an object with the AddTodoAction type.

Conclusion

To specify the return type in a TypeScript arrow function, we put a colon and the type after between the signature and the arrow.

Sometimes, we want to import two exported classes with the same name with TypeScript.

In this article, we’ll look at how to import two exported classes with the same name with TypeScript.

How to import two exported classes with the same name with TypeScript?

To import two exported classes with the same name with TypeScript, we can use the as keyword to import a member with a different name.

For instance, we write

import { Class1 } from "../location1/class1";
import { Class1 as Alias } from "../location2/class1";

to Class1 from 2 different modules.

We import the 2nd Class1 as Alias so it won’t clash with the first one.

Then we use Alias to reference the 2nd Class1.

Conclusion

To import two exported classes with the same name with TypeScript, we can use the as keyword to import a member with a different name.

To fix the "TypeScript: No index signature with a parameter of type ‘string’ was found on type ‘{ "A": string; }" error with TypeScript, we can use the keyOf operator to use the values of the keys of an object as the type.

For instance, we write

interface User {
  name: string;
  age: number;
}

const user: User = {
  name: "jane",
  age: 20,
};

const getValue = (key: keyof User) => {
  return user[key];
};

to set the getValue function’s key parameter’s type to keyof User.

This means the value of key van be 'name' or 'age'.

Then we can use key in our function to get a value from user.

Sometimes, we want to force TypeScript tsc to ignore node_modules folder.

In this article, we’ll look at how to force TypeScript tsc to ignore node_modules folder.

How to force TypeScript tsc to ignore node_modules folder?

To force TypeScript tsc to ignore node_modules folder, we can set the skipLibCheck option to true.

For instance, we write

{
  //...
  "compilerOptions": {
    "skipLibCheck": true
  }
  //...
}

to set the compilerOptions.skipLibCheck option to true in tsconfig.json to skip the node_modules folder check.

Conclusion

To force TypeScript tsc to ignore node_modules folder, we can set the skipLibCheck option to true.

Sometimes, we want to convert a TypeScript enum to object array.

In this article, we’ll look at how to convert a TypeScript enum to object array.

How to convert a TypeScript enum to object array?

To convert a TypeScript enum to object array, we can use the Object.values method.

For instance, we write

enum Colors {
  WHITE = 0,
  BLACK = 1,
  BLUE = 2,
}

const colorValueArray = Object.values(Colors);

to call Object.values with the Colors enum.

This will return an array with the values that we assigned to each enum entry.

So colorValueArray is [0, 1, 2].

Conclusion

To convert a TypeScript enum to object array, we can use the Object.values method.