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
– John Montgomery, Commented May 11, 2020 at 23:09
data[0][0] is undefined (data[0] is an empty array), which indeed isn't an array — Robin Zigmond
– Robin Zigmond, Commented May 11, 2020 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
– volume one, Commented May 12, 2020 at 10:29

Fiehra · Accepted Answer · 2022-08-24 07:11:49Z

6

You could do something like this:

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


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

edited Aug 24, 2022 at 7:11

Fiehra

8371 gold badge9 silver badges29 bronze badges

answered May 11, 2020 at 23:15

Thalaivar

23.7k5 gold badges63 silver badges71 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

elvira.genkel · Accepted Answer · 2020-05-11 23:10:21Z

3

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"
}

answered May 11, 2020 at 23:10

elvira.genkel

1,3331 gold badge6 silver badges12 bronze badges

Comments

Olimpiu POP · Accepted Answer · 2020-05-13 11:35:13Z

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, 2020 at 11:35

answered May 12, 2020 at 1:32

Olimpiu POP

5,0954 gold badges37 silver badges51 bronze badges

Comments

tobstar · Accepted Answer · 2022-08-23 18:31:45Z

0

You can just do:

yourNestedArray.flat().length > 0 ? 'some content' : 'im empty';

Flat a builtin function of the javascript Array class that flattens a multidimensional array by iterating through all nested items and concats them to a 1d array.

edited Aug 23, 2022 at 18:31

answered Aug 19, 2022 at 8:30

tobstar

234 bronze badges

2 Comments

Community Over a year ago

Your answer could be improved with additional supporting information. Please edit to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center.

tobstar Over a year ago

@Community Bot i have edit the comments.

Collectives™ on Stack Overflow

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

4 Answers 4

Comments

Comments

Comments

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

Comments

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related