ReactJS 通过对象映射

Question

I have a response like this:

I want to display the name of each object inside this HTML:

{subjects.map((item, i) => (
  <li className="travelcompany-input" key={i}>
    <span className="input-label">{ item.name }</span>
  </li>
))}   

But it throws an error of subjects.map is not a function .

First, I have to define the keys of the objects where it creates an array of keys, where I want to loop through and show the subject.names .

What I also tried is this:

{Object.keys(subjects).map((item, i) => (
  <li className="travelcompany-input" key={i}>
    <span className="input-label">key: {i} Name: {subjects[i]}</span>
  </li>
))}

Answer 1

When calling Object.keys it returns a array of the object's keys.

Object.keys({ test: '', test2: ''}) // ['test', 'test2']

When you call Array#map the function you pass will give you 2 arguments;

1. the item in the array,
2. the index of the item.

When you want to get the data, you need to use item (or in the example below keyName ) instead of i

{Object.keys(subjects).map((keyName, i) => (
    <li className="travelcompany-input" key={i}>
        <span className="input-label">key: {i} Name: {subjects[keyName]}</span>
    </li>
))}

Answer 2

You get this error because your variable subjects is an Object not Array , you can use map() only for Array.

In case of mapping object you can do this:

{ 
    Object.keys(subjects).map((item, i) => (
        <li className="travelcompany-input" key={i}>
            <span className="input-label">{ subjects[item].name }</span>
        </li>
    ))
}  

Answer 3

Map over the keys of the object using Object.keys() :

{Object.keys(yourObject).map(function(key) {
  return <div>Key: {key}, Value: {yourObject[key]}</div>;
})}

Answer 4

Use Object.entries() function.

Object.entries(object) return:

[
    [key, value],
    [key, value],
    ...
]

see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/entries

{Object.entries(subjects).map(([key, subject], i) => (
    <li className="travelcompany-input" key={i}>
        <span className="input-label">key: {i} Name: {subject.name}</span>
    </li>
))}

Answer 5

Do you get an error when you try to map through the object keys, or does it throw something else.

Also note when you want to map through the keys you make sure to refer to the object keys correctly. Just like this:

{ Object.keys(subjects).map((item, i) => (
   <li className="travelcompany-input" key={i}>
     <span className="input-label">key: {i} Name: {subjects[item]}</span>
    </li>
))}

You need to use {subjects[item]} instead of {subjects[i]} because it refers to the keys of the object. If you look for subjects[i] you will get undefined.

Answer 6

I am not sure why Aleksey Potapov marked the answer for deletion but it did solve my problem. Using Object.keys(subjects).map gave me an array of strings containing the name of each object, while Object.entries(subjects).map gave me an array with all data inside witch it's what I wanted being able to do this:

const dataInfected = Object.entries(dataDay).map((day, i) => {
    console.log(day[1].confirmed);
});

I hope it helps the owner of the post or someone else passing by.

Answer 7

I use the below Object.entries to easily output the key and the value:

{Object.entries(someObject).map(([key, val], i) => (
    <p key={i}>
        {key}: {val}
    </p>
))}

Answer 8

Also you can use Lodash to direct convert object to array:

_.toArray({0:{a:4},1:{a:6},2:{a:5}})
[{a:4},{a:6},{a:5}]

In your case:

_.toArray(subjects).map((subject, i) => (
    <li className="travelcompany-input" key={i}>
        <span className="input-label">Name: {subject[name]}</span>
    </li>
))}