The JavaScript Promise.resolve() method
The Promise.resolve(value) method returns a promise that is already fulfilled with value. It's used to wrap a plain value in a promise, to start a promise chain, or to normalize a function that might return either a value or a promise. Its counterpart is Promise.reject(reason).
Overview
Promise.resolve() creates a promise that's already settled in the fulfilled state, carrying whatever value you pass. It's a small utility with a few handy uses: wrapping a non-promise value so it can be used in promise-based code, providing an already-resolved starting point for a .then() chain, and returning a quick resolved promise from a function for consistency or in tests.
A common real use is normalizing a value that might be either a plain value or a promise. Promise.resolve(maybePromise) returns the promise unchanged if it already is one, or wraps a plain value — so downstream code can always await it without checking. (Note that async functions do this wrapping automatically, which is why you reach for Promise.resolve() less often than you might expect.)
Its mirror is Promise.reject(reason), which returns an already-rejected promise — useful for early-exit error cases in a promise-returning function. Both are mostly building blocks; in everyday code, async/await handles most of what they were once needed for.
Syntax
Promise.resolve(value)
Promise.resolve(42).then(v => console.log(v)); // 42
Promise.resolve(existingPromise); // returned as-is
Promise.reject(new Error("no")); // already-rejectedParameters
The Promise.resolve() method accepts the following parameters.
| Parameter | Description |
|---|---|
value |
The value to fulfill the promise with. If it is already a promise, it is returned unchanged. |
Example
<pre id="out" style="font:15px ui-monospace,monospace"></pre>
<script>
// normalize a value that might be a promise or not
function load(input) {
return Promise.resolve(input).then(v => 'loaded: ' + v);
}
Promise.all([load(42), load(Promise.resolve('async'))]).then(results => {
document.getElementById('out').textContent = results.join('\n');
});
// loaded: 42 / loaded: async
</script>Best practices
- Use it to wrap a plain value in a promise, or to start a
.then()chain. - Use it to normalize "value or promise" so callers can always await the result.
- Use
Promise.reject(reason)for an already-rejected promise (early error exits). - Remember async functions auto-wrap return values, so you often don't need it.