Question 223452 in Javascript Question posted in
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Javascript – how to simplify undefined check?

I’d like to simplify JSON object check for undefined values:

  {
    body: {
      data: {
        names: [
          {
            firstName: 'John'
          },
          {
            firstName: 'Johnn'
          }
        ]
      }
    }
  }

So if I do it like this then it throws an exception if names is an empty array []:

body?.data?.names[0]?.firstName

So should I go old way like this?

  if (
    body &&
    body.data &&
    body.data.names &&
    body.data.names.length > 0 &&
    body.data.names[0] &&
    body.data.names[0].firstName
  ) {
    // ....
  }
Tags:

2

Answers


  1. 0

    You can try undefined check using optional chaining (?.) and nullish coalescing (??) operators like the following way:

    const data =  {
    body: {
      data: {
        names: [
          {
            firstName: 'John'
          },
          {
            firstName: 'Johnn'
          }
        ]
      }
    }
  };

//test
const firstName = data?.body?.data?.names?.[0]?.firstName ?? 'Unknown';

console.log(firstName);//'John'

//test: undefined
const dataWithoutNames = {
  body: {
    data: {}
  }
};

const unknownName = dataWithoutNames?.body?.data?.names?.[0]?.firstName ?? 'Unknown';

console.log(unknownName);//'Unknown'
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  2. 0

    Another option, in case you need to work with complicated JSON objects, is using the Lodash JavaScript library. It offers useful functions for everyday programming tasks, all using the functional programming approach. After installing it by npm install lodash:

    const _ = require('lodash');
...
const firstName = _.get(yourData, 'body.data.names[0].firstName');

    The get function enables easy access to nested properties without the need to worry about undefined values.

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