Javascript - Appending object to JSON File

Question

I currently have an object:

var obj = {
        username: "James",
        surname: "Brandon",
        id: "[2]"
}

and I want to append it to "users.json":

[
  {    
    "username": "Andy",
    "surname": "Thompson",
    "id": [0],
  },
  {    
    "username": "Moe",
    "surname": "Brown",
    "id": [1]
  }
]

Do you know how I might be able to do this? Thanks in advance.

users.push(obj)? This is assuming users is the second array you posted. — slider
– slider, Commented Oct 29, 2018 at 22:25
Give us more detail about the output .json - is this a file to produce, is it an output? Are you running in node.js or browser? — Deian
– Deian, Commented Oct 29, 2018 at 22:26
Well you can add it, but it will not save it to the file on the server... — epascarello
– epascarello, Commented Oct 29, 2018 at 22:31
You cannot push to the end of a JSON file using push. You need to load the file, then parse it using var val = JSON.parse(textFromFile) you can then use push to push it onto the end of that val val.push({/*new object*/}), then you will need to stringify the val var newString = JSON.strigify(val) and then you finally can save newString to a file. — Get Off My Lawn
– Get Off My Lawn, Commented Oct 29, 2018 at 22:36

David · Accepted Answer · 2018-10-30 07:39:23Z

10

This answer is assuming that you are working under Node.js.

As I understand your problem you need to solve a few different programming questions.

read and write a .json file

const fs = require("fs");
let usersjson = fs.readFileSync("users.json","utf-8");

transform a json string into a javascript array
```
let users = JSON.parse(usersjson);
```
append an object to an array
```
users.push(obj);
```
transform back the array into a json string
```
usersjson = JSON.stringify(users);
```

save the json file

fs.writeFileSync("users.json",usersjson,"utf-8");

edited Oct 30, 2018 at 7:39

David

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answered Oct 29, 2018 at 22:37

PA.

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3 Comments

James Morgson Over a year ago

The only thing was that it complains that require isn't defined and I'm not sure how to include it.

epascarello Over a year ago

This answer is assuming it is node and it appears that it ain't node the OP is after.

dancus25 Over a year ago

users.push(obj) does not work, you need to convert users from any to Array first: const arr = Array.from(users);, and then you can use arr.push(obj) and so on.

David · Accepted Answer · 2018-10-29 22:55:09Z

If your code is running in the browser and users.json is an output file, I guess you already have access to its content.

Use the push() method.

Also, note the missing commas in your objects.

var obj = {
        username: "James",
        surname: "Brandon",
        id: "[2]"
};

var users = [
  {    
    "username": "Andy",
    "surname": "Thompson",
    "id": [0]
  },
  {    
    "username": "Moe",
    "surname": "Brown",
    "id": [1]
  }
];

users.push(obj);
console.log( JSON.stringify(users) );

Now that you have the updated array of objects you can upload it to the server (check this question) or offer a download to the user (check this other question).

As you have been already told, there is no way to directly update client-side a file in the server. It is also not possible to save it directly into the client filesystem.

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