How to check if a nested array is empty or not?

Question

How do I check whether a nested array is empty or not? The array looks like this when there is no data:

const data = [

              [  ]

             ]

And if it has data it looks like this:

const data = [

              [{"Product": 7  }]

             ]

To check if it is empty I am doing the following which does not work:

if (!Array.isArray(data[0][0]) || data[0][0].length === 0) {
    return "Data is empty"
}

What I don't understand is why !Array.isArray(data[0][0]) returns true, which means the nested array is not an array (which is strange because it is an array, just empty). According to the docs, Array.isArray([]) returns true so how can !Array.isArray(data[0][0] return true?
The data[0][0].length part throws an error saying "TypeError: "data[0][0] is undefined"". Why would that be the case?
That leads to the question of how to check if a nested array is empty or not?

You only have one level of nesting but you're trying to do two. Just change it to `data[0]` instead. — John Montgomery, May 11 '20 at 23:09
`data[0][0]` is `undefined` (`data[0]` is an empty array), which indeed isn't an array — Robin Zigmond, May 11 '20 at 23:11
Looks like a simple oversight. `data` is the parent array. It has one item in it which is the child array. So to access the first item of `data` (the child array) you have to do `data[0]`. I went one level too deep! — volume one, May 12 '20 at 10:29

score 3 · Answer 1 · answered May 11 '20 at 23:15

You could so something like below:

function checkIfEmpty(array) {
  return Array.isArray(array) && (array.length == 0 || array.every(checkIfEmpty));
}


console.log(checkIfEmpty([[{"name":"something"}]])); // false
console.log(checkIfEmpty([[]])); // true

score 2 · Accepted Answer · answered May 11 '20 at 23:10

data[0][0] is the first element of nested array: for first example it is undefined, for second object {"Product": 7 }. You need to check data[0] - it is first nested array, so you need the following:

if (!Array.isArray(data[0]) || data[0].length === 0) {
    return "Data is empty"
}

Olimpiu POP · Answer 3 · 2020-05-13T11:35:13.867

1

You can check whether an array is empty like this:

if (Array.isArray(a) && a.length) {
     // whatever you would like to do
}

A very comprehensive explanation you can find in this response. So, looking at your concrete question that would mean the following:

const data = [[]]

if (Array.isArray(data[0]) && data[0].length === 0) {
     // whatever you would like to do
     console.log("empty array")
}

edited May 13 '20 at 11:35

answered May 12 '20 at 01:32

Olimpiu POP

4,856
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score -1 · Answer 4 · answered May 11 '20 at 23:10

-1

Use should first apply Array.prototype.flat() an then check the length of a resulting array.

answered May 11 '20 at 23:10

Alex

4,401
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How to check if a nested array is empty or not?

4 Answers4