在地图内部映射以获取子数组

Question

I have the following data:

{
"data": {
"site": {
  "siteMetadata": {
    "siteLinks": [
      {
        "title": "title 1",
        "submenu": [
          {
            "title": "test-1",
          }
        ]
      },
      {
        "title": "title 2",
        "submenu": [
          {
            "title": "test-2",
          }
        ]
      },
      {
        "title": "title-3",
        "submenu": [
          {
            "title": "test-3",
          }
        ]
      },
      {
        "title": "title-4",
        "submenu": [
          {
            "title": "test-4",
          }
        ]
      }
    ]
  }
}

} }

and I am trying to map to get the submenu title. I have managed to get the first title working with the following code but I am struggling to get the map inside a map.

import React from "react"

const Header = props => (
<div>
    {props.siteLinks.map((item, key) => (
        <div>
            <li key={item.title}>{item.title}</li>
        </div>
    ))}
</div>
)

export default Header

Any help would be much appreciated

Answer 1

You can add second map function inside a first one

import React from 'react';

const Header = props => (
      <div>
       {props.siteLinks.map((item, key) => (
        <div key={item.title}>
            <li>{item.title}</li>
            {item.submenu.map((x)=>(
              <li key={x.title}>{x.title}</li>
            ))}
        </div>
       ))}
    </div>
)

export default Header;

Answer 2

 const Header = props => ( <div> {props.siteLinks.map((item, key) => ( <div key={`${item.title}-${key}`}> <h4>{item.title}</h4> {item.submenu && item.submenu.map((subitem, i) => ( <li key={`${item.title}-${key}-${i}`}>{subitem.title}</li> ))} </div> ))} </div> ); const res = { data: { site: { siteMetadata: { siteLinks: [ { title: "title 1", submenu: [ { title: "test-1" } ] }, { title: "title 2", submenu: [ { title: "test-2" } ] }, { title: "title-3", submenu: [ { title: "test-3" } ] }, { title: "title-4", } ] } } } }; ReactDOM.render( <Header siteLinks={res.data.site.siteMetadata.siteLinks} />, document.getElementById("root") );

 <script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.6.3/umd/react.production.min.js"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.6.3/umd/react-dom.production.min.js"></script> <div id="root"></div>

Answer 3

Something like this should work, just take the nested array and re-map its output again. I'd recommend using a unique key for each, rather than the title.

import React from 'react';
import uuid from 'uuidv4';

const Header = props => (
    <div>
        {props.siteLinks.map((item, key) => (
            <div>
                <li key={uuid()}>
                    <h2>{item.title}</h2>
                    {item.submenu.map(subitem => (
                        <p key={uuid()}>{subitem.title}</p>
                    ))}
                </li>
            </div>
        ))}
    </div>
);

export default Header;