How to check if the array data already exists in angular

Question

here's the code:

data = [
    {
        'id': 'asdja',
        'username': 'james',
    },
    {
        'id': 'asqweja',
        'username': 'rhou',
    },
    {
        'id': 'asdqweqj',
        'username': 'arianne'
    },
    {
        'id': 'qpoaksl',
        'username': 'ryan'
    }
];

I'm trying to check if username already exists.

For example if I input "james" then it should display "Username already exists"

I try to used find:

if (username === data.find((x: any) => x.username === x.username) {
 console.log('Username already exists');
} else {
 console.log('');
}

please add whatever you tried to do so far. It helps the community to understand what went wong. — Varit J Patel
– Varit J Patel, Commented Feb 28, 2020 at 1:19
Answered as per your solution and explain to you what was wrong you're doing. — Varit J Patel
– Varit J Patel, Commented Feb 28, 2020 at 1:46
@Panda, data.find return null or element, so must be if (data.find((x: any) => x.username === x.username). when you compare object, NOT compare that has the same properties, e.g. obj={a:10}; obj1={a:10}; bool equals=obj===obj2; equals is FALSE — Eliseo
– Eliseo, Commented Feb 28, 2020 at 8:31

KShewengger · Accepted Answer · 2020-02-28 01:20:20Z

5

You can use Javascript Array some for it which returns a boolean when the condition is or isn't met.

const inputName = 'james';

// You can use destructuring assignment ({ }) if you only want to use/
// extract a certain property, in our case we will only use the username
const isUserExists = data.some(({ username }) => username === inputName);

console.log(isUserExists);

answered Feb 28, 2020 at 1:20

KShewengger

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Varit J Patel · Accepted Answer · 2020-02-28 01:22:48Z

const data = [
    {
        id: 'asdja',
        username: 'james',
    },
    {
        id: 'asqweja',
        username: 'rhou',
    },
    {
        id: 'asdqweqj',
        username: 'arianne'
    },
    {
        id: 'qpoaksl',
        username: 'ryan'
    }
];

const user = data.find((x) => x.username === 'james')

if (user) {
 console.log('Username already exists');
} else {
 console.log('');
}

The issue is that find function returns the first element of the array

Hence, you will get the object back in the response and now you need to check it with the username

const user = data.find((x) => x.username === 'james')

if (user) {
 console.log('Username already exists');
} else {
 console.log('');
}

hope this helps!

sudo97 · Accepted Answer · 2020-02-28 01:28:05Z

1

What you are trying to do is lookup the data array (which is an array of objects) for a given username and want to know if it exists or not. You could simply use filter() to see if you get an empty list or not. If it returns an empty list then the username does not exist else it does.

var nameToCheck = 'james'
function checkUsername({username}) {
  return username===nameToCheck
}

var res = data.filter(checkUsername);

console.log(res===[] ? 'Username does not exists!' : 'Username already exists!');

answered Feb 28, 2020 at 1:28

sudo97

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Comments

Sameer · Accepted Answer · 2020-02-28 04:53:39Z

1

You can also directly check in if condition using filter-length

const data = [{id:'asdja',username:'james',},{id:'asqweja',username:'rhou',},{id:'asdqweqj',username:'arianne'},{id:'qpoaksl',username:'ryan'}];
let username = 'james';

if (data.filter(({ username }) => username == username).length) {
 console.log('User already exists');
} else {
  console.log('New User');
}

answered Feb 28, 2020 at 4:53

Sameer

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Comments

Ryan Gek · Accepted Answer · 2021-01-23 21:31:44Z

0

Another way (using index)

const username: string = "james";
const idx: number = data.findIndex(obj => obj.username === username);
if (idx > -1) {
// Username already exists.
} else {
// Username does not exists.

edited Jan 23, 2021 at 21:31

answered Feb 28, 2020 at 7:30

Ryan Gek

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