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.

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