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Javascript – Why is a Promise.reject returned in an async function not caught by a try-catch block inside that function?

I’m implementing an asynchronous function to fetch and show JSON data from an API.

In order to handle errors properly, I’m using a try/catch block.

But I’m getting an "Uncaught (in promise)" Error – and I don’t understand why.

This is my code:

const getData = async() => {
  const url = "https://dummyjson.com/quotees?limit=20"; // it contains a typo (quotees) intentionally
  try {
    const res = await fetch(url);
    return res.ok ? res.json() : Promise.reject(res.status);
  } catch(err) {
    console.log(err);
  }
};

getData()
  .then(d => {
    if (d) d.quotes.forEach(q => ...);
  });

The output of console.log(err) is "Uncaught (in promise) 404".

Why isn’t it simply "404"?

Tags:

2

Answers


  1. 0

    You return a rejected promise which is unhandled thus raising an error at the global scope. To use your catch block just throw:

    const getData = async() => {
  const url = "https://dummyjson.com/quotees?limit=20"; // it contains a typo (quotees) intentionally
  try {
    const res = await fetch(url);
    if(res.ok) return res.json();
    throw res;
  } catch(err) {
    if(err instanceof Response){
      console.log('response error:', err.status);
    } else {
      console.log('another error:', err);
    }
  }
};

getData();
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  2. 0

    I think you can throw the rejected promise and add a catch block to handle it.
    Something like the following should work –

    const getData = async() => {
  const url = "https://dummyjson.com/quotees?limit=20"; 
  try {
    const res = await fetch(url);
    if (!res.ok) {
      throw new Error(res.status);  
    }
    return res.json();
  } catch(err) {
    console.log(err);  
};

getData()
  .then(d => {
    if (d) d.quotes.forEach(q => ...);
  })
  .catch(err => {
    // error handling
  });
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