javascript - What is the correct way for getting data from this object in ReactJS?

Question

I've got ReactJs who is getting response from backend server. console.log(content) is looking like this:

{
    "data": {
        "dataNKS": [
            75670.99,
            75654.97,
            75943.38
        ],
        "dataMNKS": [
            37835.5,
            37827.49,
            37971.69
        ],
        "dataEKS": [
            75871.73,
            75816.11,
            76062.19
        ],
        "dataMEKS": [
            37935.86,
            37908.05,
            38031.1
        ]
    },
    "id": "32083654",
    "descr": "articleno1",
    "price": "75.284",
    "link": "/linkno1",
    "sqm": "75",
    "ppm2": "2151"
}

Now in my react app I can easily access to data with {content.price} eg. and I will get 75.284.

Now trouble I've got is when accessing content.data. I can access to data and console.log it, where data is formatted like this:

{dataNKS: Array(3), dataMNKS: Array(3), dataEKS: Array(3), dataMEKS: Array(3)}

Now my question is how to access each data and output it? Desired look in React app would be to output value of dataNKS + dataMNKS and under it dataEKS + dataMEKS eg. 75670 - 37835.5 - this is first entries of arrays dataNKS and dataMNKS. I've tried

const a = content.data;
return(
<div className ='container'>
{a.map((item, i) => (
          <li key={i}>
            {item.dataEKS}
            {item.dataMEKS}
          </li>
        ))}
</div>
);
-------Eror Cannot read property 'map' of undefined----------
<div className='container'>
          {Object.keys(a).map((keyName, i) => (
            <div key={i}>
              <strong>Name: {a[keyName]}</strong>
            </div>
          ))}
        </div>
-------Error Cannot convert undefined or null to object-------

and few other methods but without success. What is correct way of displaying data from this object?

EDIT: Requested part of getting content:

const [content, setContent] = useState([]);

useEffect(() => {
    const fetchPosts = async () => {
      const id = props.match.params.id;
      const res = await ArticleService.article(id);
      setContent(res.data);
    };
    fetchPosts();
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, []);

and after this I can console.log(content)

question from:https://stackoverflow.com/questions/65882024/what-is-the-correct-way-for-getting-data-from-this-object-in-reactjs

Answer 1

It is correct in your second code.There are only one error you need to handle:

Cannot convert undefined or null to object

you can resolve it by this:

<div className='container'>
 {a&&Object.keys(a).map((keyName, i) => (
   <div key={i}>
     <strong>Name: {a[keyName]}</strong>
   </div>
 ))}
</div>