Appending a JS array to JSON after writing to and reading the JSON

Question

I'm trying to save data to a JSON file, the first save goes fine, the second save breaks the JSON. Here is what my array looks like (simplified for example):

var myArray1 = new Array ({
  Ex1 : "Ex1",
  Ex2 : "Ex2",
  Ex3 : "Ex3"
});

I save this to JSON, which returns valid json, I read it and try to save another array like this on top of this one:

var myArray2 = new Array ({
  Ex4 : "Ex4",
  Ex5 : "Ex5",
  Ex6 : "Ex6"
});

I've tried using concat which creates this in Chrome Console:

0:
  Ex1: "Ex1"
  Ex2: "Ex2"
  Ex3: "Ex3"
  __proto__: Object
1:
  Ex4: "Ex4"
  Ex5: "Ex5"
  Ex6: "Ex6"
  __proto__: Object
length: 2
__proto__: Array(0)

I would assume using JSON.stringify now would make it valid JSON but when I save it to JSON it gives me this:

[{
    "chosenDate": "May_2019_1",
    "shiftName": "Test 1",
    "startTime": "00:00",
    "endTime": "01:00",
    "payPerHour": "1.00"
}]
[{
    "chosenDate": "May_2019_16",
    "shiftName": "Test 2",
    "startTime": "01:00",
    "endTime": "02:00",
    "payPerHour": "2.00"
}]

The first JSON was the exact same up until the first "]" so concat did nothing in the end? How can I solve this so it makes valid JSON?

I don't know if it changes anything but I'm trying to make an ionicv1 app, using the cordova-file-plugin to save JSON.

EDIT: So I'm unsure why but when trying to use my example in Chrome it works, but when running it through my app, actually putting it in a file and reading it from the file it returns the broken JSON. The process is:

create first array.
stringify it and write to json file.
read file and parse json.
create second array.
concat the arrays.
stringify and write to json.

and the file has the broken JSON. I guess somewhere in writing it or reading something is not going quite right, also setting it apart from the possible duplicate post.

Possible duplicate of [write/add data in JSON file using node.js](https://stackoverflow.com/questions/36856232/write-add-data-in-json-file-using-node-js) — ponury-kostek, May 22 '19 at 08:45
JSON files are difficult to append to (the whole file should be read, then parsed, then rewritten). I suggest using [JSONL](http://jsonlines.org/) instead - a format almost as easy to use as JSON. — Amadan, May 22 '19 at 08:49

Anurag Srivastava · Answer 1 · 2019-05-22T09:14:16.463

2

Your statement:

var myArray1 = new Array ({
  Ex1 : "Ex1",
  Ex2 : "Ex2",
  Ex3 : "Ex3"
});

Creates an array of one object, and you do this twice, so you get two arrays, containing 1 object each.

You must create the first array, then keep pushing to it.

var myArray1 = new Array({
  Ex1 : "Ex1",
  Ex2 : "Ex2",
  Ex3 : "Ex3"
});

myArray1.push({
  Ex4: "Ex4",
  Ex5: "Ex5",
  Ex6: "Ex6"
})

console.log(myArray1)

edited May 22 '19 at 09:14

answered May 22 '19 at 08:47

Anurag Srivastava

14,077
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This gives me the same result – kevinfromspace May 22 '19 at 09:05
@anurag you missed ',' after values kevin check now – Sa E Chowdary May 22 '19 at 09:13

EternalLight · Answer 2 · 2019-05-22T09:37:05.493

Allright, from your code it should look like this:

const myArray1 = new Array ({
    Ex1 : "Ex1",
    Ex2 : "Ex2",
    Ex3 : "Ex3"
});

const myArray2 = new Array ({
    Ex4 : "Ex4",
    Ex5 : "Ex5",
    Ex6 : "Ex6"
});

const mergedArray = myArray1.concat(myArray2);
// Merged array is now:
// 0:
//  Ex1: "Ex1"
//  Ex2: "Ex2"
//  Ex3: "Ex3"
//  __proto__: Object
// 1:
//  Ex4: "Ex4"
//  Ex5: "Ex5"
//  Ex6: "Ex6"

JSON.stringify(mergedArray, null, 4);

// Returns formatted JSON.
// "[
//     {
//         "Ex1": "Ex1",
//         "Ex2": "Ex2",
//         "Ex3": "Ex3"
//     },
//     {
//         "Ex4": "Ex4",
//         "Ex5": "Ex5",
//         "Ex6": "Ex6"
//     }
// ]"

I tried it in Chrome console - it returns valid JSON. Check what might be different from what you are doing.

Appending a JS array to JSON after writing to and reading the JSON

2 Answers2