Check if array undefined in React component

Question

I have a code in React component that renders match name. But sometimes current match have emty object and I can't pass this issue. Component code:

import React from 'react'
import {Link} from 'react-router-dom'

    export const MatchList  = ({ links }) => {
      if (!links.length) {
        return <p className="center">Матчей пока нет</p>
      }
    
      return (
        <table>
          <thead>
          <tr><th><a href="/add">Добавить ссылку</a></th></tr>
          <tr>
            <th>link</th>
            <th>Открыть</th>
          </tr>
          </thead>
    
          <tbody>
          { links.map((link, index) => {
            return (
              link.dataInfo1param1.length > 0 ?
              <tr key={link._id}>
                <td>{link.url}</td>
                <td>
                  Name: { link.dataInfo1param1[0][0]['odddTitle'] } <Link to={`/match/${link._id}`}>Открыть</Link>
                </td>
              </tr>
              :
              <tr key={link._id}>
                <td>{link.url}</td>
                <td>
                  <Link to={`/match/${link._id}`}>Открыть</Link>
                </td>
              </tr>
            )
          }) }
          </tbody>
        </table>
      )
    }

When link.dataInfo1param1 has an empty value I always get an error

× TypeError: Cannot read properties of undefined (reading 'length')

How I can check that this value do not exist or empty? Thanks

tmsbrndz · Accepted Answer · 2021-12-15 09:21:02Z

2

Check out optional chaining.

link.dataInfo1param1?.length > 0

answered Dec 15, 2021 at 9:21

tmsbrndz

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Comments

abhishek sahu · Accepted Answer · 2021-12-15 09:19:20Z

0

you can use ternary operator for this check as below.

       <td>
          Name: { link.dataInfo1param1?link.dataInfo1param1[0][0]['odddTitle']:null } <Link to={`/match/${link._id}`}>Открыть</Link>
        </td>

answered Dec 15, 2021 at 9:19

abhishek sahu

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Comments

Jerry · Accepted Answer · 2021-12-15 09:19:33Z

0

the simplest solution would be link.dataInfo1param1 && link.dataInfo1param1.length > 0

answered Dec 15, 2021 at 9:19

Jerry

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Comments

ali varaste pour · Accepted Answer · 2021-12-15 09:20:29Z

0

before mapping your list you can check if it is empty or not like this:

{
    links && links.map(link, index) => {//your logic}
}

answered Dec 15, 2021 at 9:20

ali varaste pour

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Comments

samix · Accepted Answer · 2021-12-15 09:31:24Z

0

there is an operator in JS you can use in these situations, optional chaining

use it like this:

link.dataInfo1param1?.length > 0

edited Dec 15, 2021 at 9:31

answered Dec 15, 2021 at 9:23

samix

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Comments

Giovanni Esposito · Accepted Answer · 2021-12-15 09:40:16Z

0

There are a lot of ways to verify if link.dataInfo1param1 is undefined. The ways I usually use are:

Triple operator, in your case would be:

link.dataInfo1param1 !== undefined && link.dataInfo1param1.length > 0 && ...

typeof operator:

typeof link.dataInfo1param1 != 'undefined' && link.dataInfo1param1.length > 0 && ...

simple check:

link.dataInfo1param1 && link.dataInfo1param1.length > 0 && ...

optional chaining operator:

link.dataInfo1param1?.length > 0 && ...

answered Dec 15, 2021 at 9:40

Giovanni Esposito

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Comments

Shawn · Accepted Answer · 2021-12-16 00:46:12Z

0

Check whether link.dataInfo1param1 exists before reading its length property

 Array.isArray(link.dataInfo1param1) && link.dataInfo1param1.length > 0

edited Dec 16, 2021 at 0:46

Shawn

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answered Dec 15, 2021 at 9:21

hellogoodnight

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