CODEWITHSUNDEEP
javascriptarrays
Bomber
Bomber

Reputation: 10957

Array spread merge array of objects

How can I merge arrays of objects using spread syntax?

My data array can be any length, I need to combine them all into mergedResults

Any ideas?

   Promise.all(apiPromises).then(data => {
                let mergedResults = []
                data.forEach(function(element) {
                    const { events } = element;

                    mergedResults[...events]

                    console.log(mergedResults)
                });
   });

Upvotes: 2

Views: 1569

Answers (2)

T.J. Crowder
T.J. Crowder

Reputation: 1074355

You can't add to an existing array with spread inside [], you can only create a new array (like concat does):

mergedResults = [...mergedResults, ...events];

...which isn't very efficient if modifying the existing array is acceptable (but is common in situations where leaving the original array alone is important, such as when programming with immutable objects).

For that reason, you might use push with spread syntax instead:

mergedResults.push(...events);

Side note: You can use destructuring in the forEach parameter list rather than as a separate statement:

Promise.all(apiPromises).then(data => {
    let mergedResults = [];
    data.forEach(({events}) => {
    // -----------^^^^^^^^
        mergedResults.push(...events);
    });
    // ...presumably do something with `mergedResults` here...
});

Perhaps even throw in for-of:

Promise.all(apiPromises).then(data => {
    let mergedResults = [];
    for ({events} of data) {
        mergedResults.push(...events);
    }
    // ...presumably do something with `mergedResults` here...
});

Or as with all array operations where you visit all elements, you can shoehorn this into reduce, but you don't gain anything by it, it just makes things more complicated:

Promise.all(apiPromises).then(data => {
    let mergedResults = data.reduce((results, {events}) => {
        results.push(...events);
        return results;
    }, []);
    // ...presumably do something with `mergedResults` here...
});

Upvotes: 3

Jonas Wilms
Jonas Wilms

Reputation: 138267

You have to push them:

  mergedResults.push(...events);

If you do:

  mergedResults[ something ]

thats just a property access.

Upvotes: 3

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