Category: TypeScript

Sometimes, we want to use Node.js require inside a TypeScript file.

In this article, we’ll look at how to use Node.js require inside a TypeScript file.

How to use Node.js require inside a TypeScript file?

To use Node.js require inside a TypeScript file, we can use the import keyword.

For instance, we write

import sampleModule = require("modulename");

or

import * as sampleModule from "modulename";

to import the modulename module in TypeScript.

Then we can compile our TypeScript project with the --module commonjs option.

Conclusion

To use Node.js require inside a TypeScript file, we can use the import keyword.

Sometimes, we want to fix the "Cannot find module" error with importing images in TypeScript React.

In this article, we’ll look at how to fix the "Cannot find module" error with importing images in TypeScript React.

How to fix the "Cannot find module" error with importing images in TypeScript React?

To fix the "Cannot find module" error with importing images in TypeScript React, we should declare the .jpg module in a TypeScript type definition file.

For instance, we write

declare module '*.jpg';

in index.d.ts in the TypeScript project folder to let the TypeScript compiler know that .jpg files can imported into our project directly.

Conclusion

To fix the "Cannot find module" error with importing images in TypeScript React, we should declare the .jpg module in a TypeScript type definition file.

Sometimes, we want to check against custom type with ‘typeof’ in TypeScript.

In this article, we’ll look at how to check against custom type with ‘typeof’ in TypeScript.

How to check against custom type with ‘typeof’ in TypeScript?

To check against custom type with ‘typeof’ in TypeScript, we can use typeof to get the type of any variable.

For instance, we write

const fruit = ["apple", "banana", "grape"] as const;
type Fruit = typeof fruit[number];
const isFruit = (x: any): x is Fruit => fruit.includes(x);

const myFruit = "pear";
if (isFruit(myFruit)) {
  //...
}

to define the Fruit type by creating a union of the values in the fruit array with typeof fruit[number].

Then we create the isFruit type guard that check if x is of type Fruit with fruit.includes(x).

And then we call isFruit with myFruit to check if myFruit is a Fruit.

Since 'pear' isn’t in fruit, it’s not a Fruit.

Conclusion

To check against custom type with ‘typeof’ in TypeScript, we can use typeof to get the type of any variable.

Sometimes, we want to use getters or setters in interface definition with TypeScript.

In this article, we’ll look at how to use getters or setters in interface definition with TypeScript.

How to use getters or setters in interface definition with TypeScript?

To use getters or setters in interface definition with TypeScript, we can implement an interface property with a class with getters and setters.

For instance, we write

interface IExample {
  name: string;
}

class Example implements IExample {
  private _name: string = "jane";

  public get name() {
    return this._name;
  }

  public set name(value) {
    this._name = value;
  }
}

const example = new Example();

to create the Example class that implements the IExample interface.

In it, we have the name getter and setter which gets and sets the value of the _name instance variable respectively.

We defined the getter with get and the setter with set.

Conclusion

To use getters or setters in interface definition with TypeScript, we can implement an interface property with a class with getters and setters.

Sometimes, we want to create an async constructor functions in TypeScript.

In this article, we’ll look at how to create an async constructor functions in TypeScript.

How to create an async constructor functions in TypeScript?

To create an async constructor functions in TypeScript, we can create a factory method.

For instance, we write

class MyClass {
  private mMember: Something;

  private constructor() {}

  public static CreateAsync = async () => {
    const me = new MyClass();
    me.mMember = await SomeFunctionAsync();
    return me;
  };
}

to create the MyClass class that has a private constructor.

We use it to create a MyClass instance inside the CreateAsync function.

The function is static so we don’t need to instantiate MyClass to call it.

We return me which is the resolve value of the promise returned by CreateAsync.

Then we can use it by writing

const m = await MyClass.CreateAsync();

in an async function.

Conclusion

To create an async constructor functions in TypeScript, we can create a factory method.