Why does JSON.stringify() not work on this array?

Question

I have an array which is declared like this:

array = [];

and has values as shown below -

....
ChIJOaegwbTHwoARg7zN_9nq5Uc:"ChIJOaegwbTHwoARg7zN_9nq5Uc"
ChIJXTwCdefHwoAR9Jr4-le12q4:"ChIJXTwCdefHwoAR9Jr4-le12q4"
....

These values are printed when I do console.log(array);

When I try to do a JSON.stringify(array), it does not seem to work. I want to store this array in localStorage using localStorage.setItem().

I tried an example like in this in the browser console:

var arr=[]
arr[0] = 1
arr[1] = 2
JSON.stringify(arr);

And the above example worked perfectly fine.

Please provide your inputs, I have been stuck at this for hours.

Step 1: Learn the difference between arrays and objects. There is no such thing as an associative array in JavaScript. You added arbitrary custom properties to an array, but those are not _elements_ of the array, so they don’t get serialized by JSON.stringify. — CBroe, Apr 06 '18 at 06:51
Both Objects and Arrays are associative, only that they keys are permitted to only be or be convertible to Strings and Numbers respectively. — Dan D., Apr 06 '18 at 06:54
Possible duplicate of [JavaScript associative array to JSON](https://stackoverflow.com/questions/4425289/javascript-associative-array-to-json) — Andreas, Apr 06 '18 at 07:00

score 1 · Answer 1 · answered Apr 06 '18 at 06:53

1

You are trying to assign values in array like objects ; index can only be o,1,2 etc. not the strings like you have used. If you must do this, create an array of objects

answered Apr 06 '18 at 06:53

Shubham Shekhar

11
1

score 1 · Answer 2 · answered Apr 06 '18 at 06:57

the problem is that you are trying to set the array index as strings 'ChIJOaegwbTHwoARg7zN_9nq5Uc' and 'ChIJXTwCdefHwoAR9Jr4-le12q4' and although the browser seems to print it in the console, but array considers only integer keys as valid indices, so if you try to print array.length, it will print 0 and hence operations such as JSON.stringify(array) don't return you anything

var array = [];
array['ChIJOaegwbTHwoARg7zN_9nq5Uc'] = "ChIJOaegwbTHwoARg7zN_9nq5Uc";
array['ChIJXTwCdefHwoAR9Jr4-le12q4'] = "ChIJXTwCdefHwoAR9Jr4-le12q4";
console.log(array);
console.log(array.length)

What you need is not an array but an object

var obj = {};
obj['ChIJOaegwbTHwoARg7zN_9nq5Uc'] = "ChIJOaegwbTHwoARg7zN_9nq5Uc";
obj['ChIJXTwCdefHwoAR9Jr4-le12q4'] = "ChIJXTwCdefHwoAR9Jr4-le12q4";
console.log(obj);
console.log(JSON.stringify(obj))

score 0 · Answer 3 · answered Apr 06 '18 at 06:52

0

That's not an array, but an object. Objects don't stringify as well as arrays do.

Basically:

String = 'This is a string'

Array = [
  'This is a string',
  'And so is this'
]

Object = {
  firstString  : 'This is a string',
  secondString : 'And so is this.'
}

answered Apr 06 '18 at 06:52

Breki Tomasson

207
2
11

Both do fine, but only if their contents stringify. – Dan D. Apr 06 '18 at 06:54

score 0 · Answer 4 · answered Apr 06 '18 at 06:54

This works for me in a plunker.

let array = [];
array.push({"ChIJOaegwbTHwoARg7zN_9nq5Uc":"ChIJOaegwbTHwoARg7zN_9nq5Uc"});
array.push({"ChIJXTwCdefHwoAR9Jr4-le12q4":"ChIJXTwCdefHwoAR9Jr4-le12q4"});
console.log(JSON.stringify(array));

If you do a console.log(array), you should see something like this:

Why does JSON.stringify() not work on this array?

4 Answers4