An Exercise with Debugging and Promises

Debugging skills are one of the hardest to gain as someone new to development, so I thought I'd take the time to share some of the exercises that stumped me. Give this one a try!

You have two functions:

1. getResult returns a Promise with a 50% chance to succeed and a 50% chance to reject.

2. testGetResult calls getResult and logs the output once.

Here is the implementation that was given to you:

getResult

getResult is an async function that returns a Promise. The Promise will either reject or resolve in 1000 miliseconds, and whether it rejects or resolves depends on a variable generated. The variable will have a value between -0.5 to 0.5; in other words, there is a 50% chance of the variable being positive. If the variable is negative, it rejects. Simple, right?

const getResult = async () => {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      let number = Math.random() - 0.5
      if (number < 0) { reject("failure") }
      resolve("success")
    }, 1000)
  })
}

getTestResult is even more simple.
It initiates a variable called result and simply gets the Promise from getResult(). It will then log whether it succeeded or not.

getTestResult

async function testGetResult() {
  let result = await getResult()

  result.then((res) => console.log(res))
        .catch((err) => console.log(err))
}

The Issue

When running this example, node throws an error:

node:internal/process/promises:246
          triggerUncaughtException(err, true /* fromPromise */);
          ^

[UnhandledPromiseRejection: This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). The promise rejected with the reason "failure".] {
  code: 'ERR_UNHANDLED_REJECTION'
}

What went wrong?

I'll update the post with an answer in a few days :)

Update 08/01

Hint: what is the type being returned from getResult()?