Check if value exists in JSON Object

Question

I am learning NodeJS . I am using a JSON Object to check if a user is present.

This is my JSON (users.json):

{
    "users": [{
        "fname": "Robert",
        "lname": "Downey Jr.",
        "password": "ironman"
    }, {
        "fname": "Chris",
        "lname": "Evans",
        "password": "cap"
    }, {
        "fname": "Chris",
        "lname": "Hemsworth",
        "password": "thor"
    }, {
        "fname": "Jeremy",
        "lname": "Renner",
        "password": "hawk"
    }]
}

Now I want to pass the fname value of one entry and see if it exists in the JSON Object.

This is what I'm doing :

var file = JSON.parse(fs.readFileSync('users.json', 'utf8'));
for (eachUser in file.users) {
            console.log(eachUser.fname);
        }

But I do not get the fname values but just undefined . I don't know what I am doing wrong.

Also is there a way to find if the value exists without having to iterate over the JSON Object ?

score 0 · Answer 1 · answered Jul 07 '15 at 16:11

0

if ( typeof file !== 'undefined' && file )
{
   //do stuff if file is defined and not null
}

answered Jul 07 '15 at 16:11

NiVeR

9,644
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Or shorter: `if (file != null)`. – Felix Kling Jul 07 '15 at 16:12
I want to check if the value such as 'Chris' , 'Robert' , exists in the JSON Object. Not to check if file is null or not.. – v1shnu Jul 07 '15 at 16:14
Before those can exist, the file must exist. Then you can nest into it. – NiVeR Jul 07 '15 at 16:15

Kristján · Accepted Answer · 2015-07-07T16:19:38.200

The problem is that eachUser gets set to each index in the array - not the object at that index. If you log just eachUser, you'll see

Instead, pull out the object first, and then gets its fname

for (index in file.users) {
  console.log(file.users[index].fname)
}

Here's a demo.

If you want to do this lookup without iterating through the array, you can re-shape your data into an object with fname as the key, so it would look like:

{
  "Robert": {
    "fname": "Robert",
    "lname": "Downey Jr.",
    "password": "ironman"
  },
  "Chris": {
    "fname": "Chris",
    "lname": "Evans",
    "password": "cap"
  },
  "Jeremy": {
    "fname": "Jeremy",
    "lname": "Renner",
    "password": "hawk"
  }
}

Of course, then either you won't be able to store any duplicate first names, or your need to make the values arrays.

Yup ! this works. But can this be done without the loop. Just asking to see if there are any other ways of doing this. — v1shnu, Jul 07 '15 at 16:19

score -1 · Answer 3 · edited May 23 '17 at 12:29

-1

You have an issue in your iteration statement:

for (eachUser in file.users)

Feel free to use one the foreach statements described in this post such as:

file.users.forEach(function(user) {
    console.log(user.fname);
});

Cheers

edited May 23 '17 at 12:29

Community

1
1

answered Jul 07 '15 at 16:10

POZ

583
4
11

can u reframe your answer ? I do not get where this applies in here. – v1shnu Jul 07 '15 at 16:12

Check if value exists in JSON Object

3 Answers3