Return different objects using map without pushing into array-CodePudding

The following code in JavaScript:

const mixedObjects = [1,2,3].map(num => {
    return { a: 'always same' }
});

returns the following result:

[
  {a: 'always same'},
  {a: 'always same'},
  {a: 'always same'}
]

I want to return the following without declaring an empty array outside and then pushing into it. So do it all inside the map. Is this possible?

What I want to return:

[
  {a: 'always same'},
  {b: 1},
  {a: 'always same'},
  {b: 2},
  {a: 'always same'},
  {b: 3}
]

CodePudding user response：

Use Array.flatMap(), and return a tuple of the 2 objects on each iteration. The flatMap would create a flattened array of objects.

const mixedObjects = [1,2,3].flatMap(b => {
  return [{ a: 'always same' }, { b }]
});

console.log(mixedObjects);

CodePudding user response：

You can combine map and flat methods:

const mixedObjects = [1,2,3].map(num => {
    return [{ a: 'always same' }, {b: num}];
}).flat();

P. S. Or use flatMap method as suggested by Ori Drori.

CodePudding user response：

... reduce based solutions work as well ...

console.log(
  [1,2,3].reduce((result, b) =>
    [...result, { a: 'always same' }, { b }] , []
  )
);
console.log(
  [1,2,3].reduce((result, b) =>
    result.concat({ a: 'always same' }, { b }), []
  )
);
console.log(
  [1,2,3].reduce((result, b) => {
  
    result.push({ a: 'always same' }, { b });
    return result;

  }, [])
);

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