A Javascript promise that perpetually stays in a pending state

Question

A Javascript promise that perpetually stays in a pending state

Utilizing the rotateByDegrees function from a library called node-poweredup within a typescript project:

motor.rotateByDegrees(20,10).then(function(value) {console.log("test");}, function(value) {console.log("error");});

Expecting to see "test" after successful completion, however, the promise remains unresolved. When using await, it gets stuck on the await line indefinitely. Attempting to replicate the syntax utilized in the rotateByDegrees function:

let promise = new Promise((resolve) => { return resolve(); });

results in a compilation error:

error TS2794: Expected 1 arguments, but got 0. Did you forget to include 'void' in your type argument to 'Promise'?

I can get it to compile and function as anticipated with resolve(true), but how is it compiling in the library then? Is my understanding of promises incorrect? Could this be related to a TypeScript feature or possibly a bug in the library? As a newcomer to JavaScript, I want to avoid over-complicating things by including irrelevant information. If you could provide insight into what I might be overlooking and suggestions for debugging this issue, I would be able to offer any necessary details.

javascript typescript ecmascript-6

Answer 1

Answer №1

After receiving some helpful feedback, I was able to narrow down the issue to the compilation of the library. Instead of using a pre-compiled binary, I had to compile the library myself using electron-rebuild in order to get the bluetooth adapter to work properly. Here is the test I conducted:

git clone https://github.com/nathankellenicki/node-poweredup.git
cd node-poweredup
npm install
npm run build

The compilation process went smoothly without any errors. I then created a test file with the following content:

const PoweredUP = require("node-poweredup");

const poweredUP = new PoweredUP.PoweredUP();
poweredUP.scan(); // Initiating hub scan

console.log("Looking for Hubs...");

poweredUP.on("discover", async (hub) => { // Waiting for hubs to be discovered

    await hub.connect(); // Establishing connection to hub
    console.log(`Connected to ${hub.name}!`);

    const motorA = await hub.waitForDeviceAtPort("A"); // Ensuring a motor is plugged into port A
    motorA.rotateByDegrees(20,10).then(function(value) {console.log("test");});

});

As expected, when running the test file, I obtained the following output:

node-poweredup$ node test.js 
Looking for Hubs...
Connected to MyHub2!
test
Connected to MyHub3!
test

However, when I modified the first line to use my self-compiled binary as follows:

const PoweredUP = require(".");

The output changed to:

node-poweredup$ node test.js 
Looking for Hubs...
Connected to MyHub2!
Connected to MyHub3!

Although this doesn't provide a complete solution, it does give me a clue about where to start investigating the discrepancy in compilation results on my machine.

Answer 2

After receiving some helpful feedback, I was able to narrow down the issue to the compilation of the library. Instead of using a pre-compiled binary, I had to compile the library myself using electron-rebuild in order to get the bluetooth adapter to work properly. Here is the test I conducted:

git clone https://github.com/nathankellenicki/node-poweredup.git
cd node-poweredup
npm install
npm run build

The compilation process went smoothly without any errors. I then created a test file with the following content:

const PoweredUP = require("node-poweredup");

const poweredUP = new PoweredUP.PoweredUP();
poweredUP.scan(); // Initiating hub scan

console.log("Looking for Hubs...");

poweredUP.on("discover", async (hub) => { // Waiting for hubs to be discovered

    await hub.connect(); // Establishing connection to hub
    console.log(`Connected to ${hub.name}!`);

    const motorA = await hub.waitForDeviceAtPort("A"); // Ensuring a motor is plugged into port A
    motorA.rotateByDegrees(20,10).then(function(value) {console.log("test");});

});

As expected, when running the test file, I obtained the following output:

node-poweredup$ node test.js 
Looking for Hubs...
Connected to MyHub2!
test
Connected to MyHub3!
test

However, when I modified the first line to use my self-compiled binary as follows:

const PoweredUP = require(".");

The output changed to:

node-poweredup$ node test.js 
Looking for Hubs...
Connected to MyHub2!
Connected to MyHub3!

Although this doesn't provide a complete solution, it does give me a clue about where to start investigating the discrepancy in compilation results on my machine.

A Javascript promise that perpetually stays in a pending state

Answer №1

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