Merging many arrays from Promise.all

Question

When Promise.all completes it returns an array of arrays that contain data. In my case the arrays are just numbers:

[
    [ 1, 4, 9, 9 ],
    [ 4, 4, 9, 1 ],
    [ 6, 6, 9, 1 ]
]

The array can be any size.

Currently I'm doing this:

let nums = []
data.map(function(_nums) {
    _nums.map(function(num) {
        nums.push(num)
    })
})

Is there an alternative way of doing this? Does lodash have any functions that are able to do this?

Answer 1

ES2019 introduced Array.prototype.flat which significantly simplifies this to:

const nums = data.flat();

const data = [
  [ 1, 4, 9, 9 ],
  [ 4, 4, 9, 1 ],
  [ 6, 6, 9, 1 ]
];

const nums = data.flat();

console.log(nums);

---

_{Original Answer}

Use reduce and concat:

data.reduce(function (arr, row) {
  return arr.concat(row);
}, []);

Or alternatively, concat and apply:

Array.prototype.concat.apply([], data);

Answer 2

I would do as follows;

var a = [
    [ 1, 4, 9, 9 ],
    [ 4, 4, 9, 1 ],
    [ 6, 6, 9, 1 ]
],
    b = [].concat(...a)

console.log(b)