How To Fix Promise Not Resolved Errors in JavaScript

Promises are a cornerstone of asynchronous JavaScript, but sometimes promises do not resolve or appear to hang. This can break your application flow and cause data not to load. Understanding why promises fail to resolve and how to handle them properly is crucial for reliable asynchronous programming.

---

1. Understand the Problem

• A promise represents a value that may be available now, later, or never.
• Common causes of unresolved promises:
  • Forgetting to call resolve() inside the promise
  • Errors thrown inside the promise without a catch
  • Missing return statements in chained promises
  • Improper usage of async/await

Example of a promise that never resolves:

const myPromise = new Promise((resolve, reject) => {
  // missing resolve call
});

---

2. Always Call resolve() or reject()

• Ensure the promise calls resolve() when successful:

const fetchData = new Promise((resolve, reject) => {
  setTimeout(() => {
    resolve('Data loaded');
  }, 1000);
});

fetchData.then((data) => console.log(data)); // ✅ Data loaded

• Use reject() to handle failures explicitly.

---

3. Handle Errors Properly

• Uncaught errors inside promises prevent resolution:

const faultyPromise = new Promise((resolve, reject) => {
  throw new Error('Oops'); // Promise will reject
});

faultyPromise
  .then((data) => console.log(data))
  .catch((error) => console.error('Error:', error));

• Always attach a .catch() to handle rejections.

---

4. Return Promises in Chains

• If you return a promise inside a .then() chain, it must be returned to continue the chain:

fetchData()
  .then((data) => {
    return processData(data); // ✅ returning ensures the chain continues
  })
  .then((result) => console.log(result));

• Missing return can break the chain and prevent resolution.

---

5. Use Async/Await Properly

• Use async functions to simplify promise handling:

async function loadData() {
  try {
    const data = await fetchData();
    console.log(data);
  } catch (error) {
    console.error('Error:', error);
  }
}
loadData();

• await pauses execution until the promise resolves, making asynchronous code easier to manage.

---

6. Debugging Tips

• Add console.log statements inside promises to check execution.
• Ensure asynchronous operations like setTimeout, fetch, or APIs are correctly implemented.
• Check for missing resolve or reject calls.
• Verify that promise chains are properly returned and handled.

---

7. Best Practices Summary

1. Always call resolve() or reject() in promises.
2. Attach .catch() to handle errors.
3. Return promises in .then() chains to ensure proper resolution.
4. Use async/await for cleaner asynchronous code.
5. Debug using console.log and verify execution paths.

By following these practices, promises will resolve as expected, ensuring smooth asynchronous operations in your JavaScript applications.

---

Citations

Internal: https://savanka.com/category/savanka-helps/
External: https://developer.mozilla.org/en-US/docs/Web/JavaScript