在Javascript / React中将对象转换为数组

Question

Using REST, I am retrieving an object( JSON format) which is to be converted to an array so that it can be inserted into a table.

This is done in the rendering function of React.

The input is updated every N minutes from the back-end.

How do I convert an object to an array?

I need o nly the values, not the keys , since the keys are already present as column values beforehand in the table itself.

Answer 1

You can use Object#values (ECMAScript 2017), but it's not supported by IE (see browser's compatibility ).

Note: The ECMAScript 6 specification defines in which order the properties of an object should be traversed. This blog post explains the details .

 const map = { a: 1, b: 2, c: 3 }; const result = Object.values(map); console.log(result); 

If you need to support IE, you can use Object#keys with Array#map :

 const map = { a: 1, b: 2, c: 3 }; const result = Object.keys(map).map((key) => map[key]); console.log(result); 

Answer 2

I am not sure by map you mean the Map object or an ordinary JS object. However, just for variety I would like to mention that the Map objects are mostly (probably always) stringified like JSON.stringify([...myMap]) . So if you happen to receive a Map object in JSON data may be you should do something like;

 var myMap = new Map().set(1,"hey").set(2,"you"), mapData = JSON.stringify([...myMap]), values = JSON.parse(mapData).map(d => d[1]); console.log("mapData:",mapData); console.log("values:",values); 

Answer 3

You can set initial value as array firstly. See this example:

const [conversations, setConversations] = useState([]); // fianal data is array

useEffect(() => {
    const fetchConversations = async () => {
       const res = await axios.get("/conversations/" + user._id);              
       setConversations(res.data);              
    };
    fetchConversations();
  }, [user._id]);

res.data convert to array by using useState([]) as initial value and convert to object by using useState({}) .

And map this array:

return (
    <>
       {conversations.map((conv) => 
            (<Conversations key={conv._id} conversation={conv} />))}
    </>
)

Answer 4

You can set initial value as array firstly. See this example:

const [conversations, setConversations] = useState([]); // fianal data is array

useEffect(() => {
    const fetchConversations = async () => {
       const res = await axios.get("/conversations/" + user._id);              
       setConversations(res.data);              
    };
    fetchConversations();
  }, [user._id]);

res.data convert to array by using useState([]) as initial value and convert to object by using useState({}) .

And

return( {conversations.map((conv) => ( ))} )