It's possible that the "device.interfaces" variable has not been defined

I am currently working on creating a USB driver in TypeScript using the libusb library to adjust my keyboard lighting. However, I encountered an issue where I received a 'possibly undefined' error when trying to retrieve the interface number. The code is running on Windows, but it's identical to a tutorial I followed that was designed for Linux.

Below is the snippet of the code:

import * as usb from 'usb';

const VID = 0X0C45;
const PID = 0x672E;
const IN = 1;

const main = async () => {

    const device = usb.findByIds(VID, PID);

    console.log(device);

    device?.open();

    const deviceInterface = device?.interfaces[IN]; // Issue occurs here
    
    console.log(deviceInterface);
}

main();

Any suggestions on how to address this problem?

It seems adding a "?" can resolve the issue, but the compiler throws an error saying ": expected".

typescript

Answer №1

It seems that the issue arises when you add another question mark (?) and encounter the error ": expected", indicating TypeScript interprets it as a ternary statement.

device?.interfaces ? [IN] : 'foo'

Instead of this, you should perform an additional null check in your code.

To resolve this problem, you can create your own null check using an if statement like this:

const deviceInterface = device?.interfaces;
if(deviceInterface){
    const myInterface = deviceInterface[IN]
    console.log(myInterface);
}

You can see the corrected code on the TypeScript Playground.

Another solution, mentioned by @JaredSmith in the comments, is to use the correct syntax for null checking arrays:

device?.interfaces?.[IN]

You can view the complete corrected code on the TypeScript Playground.

Similar questions

If you have not found the answer to your question or you are interested in this topic, then look at other similar questions below or use the search

Attempting to clear the value of a state property using the delete method is proving to be ineffective

Within my React-component, there exists an optional property. Depending on whether this property is set or not, a modal dialog is displayed. Therefore, when the modal should be closed/hidden, the property must not be set. My state (in simplified form): i ...

javascriptreactjstypescriptresharper

Make sure to call super.onDestroy() in the child component before overriding it

I find myself with a collection of components that share similar lifecycle logic, so I decided to create a base component that implements the OnDestroy interface. abstract class BaseComponent implements OnDestroy { subscriptions = new Array<Subscript ...

angulartypescriptinheritance

What are the issues causing trouble for my modules, services, and more in Angular ^17?

As I was going through the themes, I couldn't find a similar question. My issue revolves around Angular's inability to locate modules and services that are created using "ng g". Everything seems to be correctly set up, but errors or warnings keep ...

angulartypescriptservicecommentsjsdoc

Using React with Typescript: Can the parent component access data fetched from a nested child component?

Can I access data retrieved from a child component (using a graphql query) in a parent component? For example, how can I use the data fetched by React-component-4 in React-component-1? Is there a way to do this or do I have to duplicate the data fetching ...

reactjstypescriptgraphql

Remove a record from Angular 2 Firebase collection

I've been searching extensively for a solution to this problem. Despite following the documentation on AngularFire 2 and Angular 2, I am unable to find a working answer. My goal is simply to delete a specific entry in my Firebase database using its un ...

angulartypescriptfirebasefirebase-realtime-databasekey

The sequence of initializing test hooks in inconsistent playwright tests

My testing framework setup looks something like this: test.describe("...", () => { let p: Page; test.beforeEach(async({browser}) => { p = await (await browser.newContext()).newPage(); } test(...); test(...); test.aft ...

javascripttypescripttestingplaywright

Utilizing Typescript to define key-value pairs within a structured form

I've been creating a form structure that's functioning smoothly, but I've encountered an interesting issue with field validation in the validation part. While my Visual Code is pointing out that 'required2' in the phone constant n ...

typescripttyping

Bring in TypeScript property from an external scope into the current scope

I am encountering an issue with my TypeScript code. Inside the anonymous functions, I am unable to change the properties of the class because they are out of scope. Is there a way to pass them in so that they can be modified? class PositionCtrl { ...

javascriptjqueryangularjstypescript

Explaining the union type using a list of data types

Is there a way to create a union type that strictly limits values to 'a', 'b', 'c' when using a list like const list: string[] = ['a', 'b', 'c']? I know one method is: const list = ['a' ...

typescript

Utilizing AWS CDK to Define StackProps Input Variables

Recently, I have started using the AWS CDK and encountered a challenge. I want to allow end users to define custom input variables when using my AWS CDK without having to edit the entire code. While I have been able to work with standard types such as stri ...

typescriptamazon-web-servicesaws-cdk

How can I provide type annotations for search parameters in Next.js 13?

Within my Next.js 13 project, I've implemented a login form structure as outlined below: "use client"; import * as React from "react"; import { zodResolver } from "@hookform/resolvers/zod"; import { signIn } from "n ...

typescriptnext.jsnext.js13react-typescript

Error thrown due to syntax issues in react.d.ts declaration file in TypeScript

Currently, I am attempting to integrate react with typescript in my project. However, typescript is generating syntax errors for the react.d.ts file sourced from Github: https://github.com/DefinitelyTyped/DefinitelyTyped/tree/master/react The encountered ...

javascriptreactjstypescript

Typescript controller inheritance leading to Error: $injector:unpr Unknown Provider due to minification

LATEST UPDATE: 2019/07/16 The issue I am facing is actually a result of misusing $inject. Instead of declaring it as private $inject in api-service.ts, it should have been public static $inject = [...]. During the minification process, explicit injection ...

angularjstypescriptminifyangularjs-controllergrunt-contrib-uglify

Is there a way to identify the accurate or incorrect array element and modify the component color accordingly?

Upon reviewing the question alternatives, I encountered a problem where clicking on one of the buttons correctly indicated whether it was the correct or incorrect answer by changing its color. However, the issue is that all buttons are being affected by th ...

reactjstypescriptstyled-componentstsxreact-tsx

Sending a XML file from a Vue application to an ASP.NET Core backend using axios

I'm encountering difficulties when trying to upload an xml file using axios to my asp .net server. Below is the code snippet I am using on the vue side to retrieve and upload the xml file: uploadXmlFile(file: any) { const rawFile = new XMLHttpRequ ...

javascriptc#typescriptvue.jsasp.net-core

Tips for managing the data type of a bound value through ngModel: preventing number distortion to string

I posted a query and managed to solve it. However, I observed that even though the provided data consists of objects defined like this: export interface GisPoint { e: number; n: number; } when a user inputs a value, the original content changes from { e: ...

angulartypescriptngmodel

Invoking a parent method from a child component in a TypeScript and React application

I'm facing an issue where I am unable to call a method from a parent component in my child component. The method in the parent element is not being triggered when the child component tries to call it. This problem is showcased in a simple example with ...

reactjstypescript

Does anyone know how to retrieve the application version or import the package.json file? Can't seem to find the solution on

I need to display the version from the package.json file in my Angular application. To import it, I allowed importing json by adding a few extra lines in tsconfig.json: { "compilerOptions": { "module": "commonjs", ...

jsonangulartypescript

What strategies can I use to preserve type narrowing when utilizing the Array.find method?

Within the code snippet below, I am encountering a typescript compilation error specifically in the Array.find method. Despite checking that `context.params.id` is not `undefined`, my type seems to lose its narrowing. I'm puzzled as to why this type ...

typescript

Do we need to import Vue in every component when using Nuxt with TypeScript?

I recently integrated TypeScript into Nuxt using the guidelines provided in the documentation: However, I have a specific question regarding component setup. Should I always include import vue from "vue" and export default Vue.extend ({}); in al ...

typescriptvue.jsvuejs2nuxt.js