Mapping an array while making an AJAX call returns undefined user data. How can I wait for the async call to complete? Example:
const entities = [
{ key: 'X', ids: [1, 2] },
{ key: 'Y', ids: [3, 4] }
];
function compileData() {
return entities.map(item => ({
key: item.key,
users: loadUsers(item.ids, result => result)
}));
}
From my personal experience, the root of the problem lies in the fact that the asynchronous loadUsers function doesn’t hold up the mapping process the way you might expect. I solved a similar problem by restructuring the code so that it iterates through each entity with a for…of loop instead of directly mapping over the array. This allowed me to await each call to loadUsers individually, ensuring the data is fully fetched before proceeding. Although it may require rewriting some parts of your logic, this approach guarantees that every asynchronous request has been completed before you use the results.
One alternative to consider is ensuring that the loadUsers function consistently returns a promise. From my experience, wrapping asynchronous call logic in a promise and then awaiting its resolution within an async iteration can lead to more predictable results. This might involve restructuring the code to avoid directly mapping over the array and instead using an async function with proper error handling. Adjusting the design in this way helped resolve similar issues with undefined values in asynchronous mapping in my projects.
In my experience, the easiest way to tackle this issue is to convert your function into an async function and use Promise.all inside it. That way you can have your array mapping waiting for each asynchronous call to resolve before continuing. I remember dealing with similar problems where I initially tried to force synchronous behaviour, but using async/await yielded a cleaner solution. It is important to remember that mapping directly over the array without handling promises will always return unresolved promises, which explains the undefined results you observed.
A possible solution is to ensure that your AJAX call returns a promise so that you can correctly await its result. In my experience, wrapping your mapping logic inside an async function and using Promise.all to wait for all asynchronous actions helps manage the issue. For example, you can transform your code so that you’re awaiting the result from loadUsers, thereby resolving each promise before proceeding. This approach mitigates the undefined outputs caused by unresolved promises when mapping asynchronously over an array.
hey, maybe try wrapping your loadUsers calls inside promises and then await them in an async function. this way you get full resolution before the next step. could also check if loadUsers actually returns a promise or not, cause that can lead to undefined issues. thanks!