CODEWITHSUNDEEP
javascriptreactjs
Leo Jiang
Leo Jiang

Reputation: 26085

Return multiple React elements in a method without a wrapper element

I'm trying to return multiple React elements from a helper method. I could solve it simply by moving around some code, but I'm wondering if there's a cleaner way to solve it. I have a method that returns part of the render method, and that functions needs to return both a React element and some text. It's clearer through an example:

class Foo extends React.Component {
  _renderAuthor() {
    if (!this.props.author) {
      return null;
    }

    return [
      ' by ',
      <a href={getAuthorUrl(this.props.author)}>{this.props.author}</a>,
    ]; // Triggers warning: Each child in an array or iterator should have a unique "key" prop.

  render() {
    return (
      <div>
        {this.props.title}
        {this._renderAuthor()}
      </div>
    );
  }
}

I know the render method has to return exactly 1 React element. Using a helper method like this would trigger a warning, and fixing the warning (by adding keys) would make the code too convoluted. Is there a clean way to do this without triggering a warning?

Edit:

Another use case:

render() {
  return (
    <div>
      {user
        ? <h2>{user.name}</h2>
          <p>{user.info}</p>
        : <p>User not found</p>}
    </div>
  );
}

Edit 2:

Turns out this isn't possible yet, I wrote about 2 workarounds here: https://www.wptutor.io/web/js/react-multiple-elements-without-wrapper

Upvotes: 20

Views: 21980

Answers (10)

Tom Davies
Tom Davies

Reputation: 899

It's not currently possible to do this without some sort of workaround like wrapping everything in another component, since it ends up with the underlying React code trying to return multiple objects.

See this active Github issue where support for this is being considered for a future version though.

Edit: You can now do this with Fragments in React 16, see: https://reactjs.org/blog/2017/11/28/react-v16.2.0-fragment-support.html

Upvotes: 9

Pataar
Pataar

Reputation: 661

Support has been added using the Fragment component. This is a first-class component.

So you can now use:

render() {
  return (   
    <React.Fragment>
      <ChildA />
      <ChildB />
      <ChildC />
    </React.Fragment>
  );
}

For more information visit: https://reactjs.org/blog/2017/11/28/react-v16.2.0-fragment-support.html

Upvotes: 14

Faaiz Khan
Faaiz Khan

Reputation: 332

Perhaps a more simple way would be to rethink how you're architecting your application. However, in a more simple way.

You're triggering the warning because you're trying to render from an array and not react elements but directly html. In order to approach this, you would have to do 

{this._renderAuthor().map(
    (k,i) => (React.addons.createFragment({k}))
    )  }

React addons createFragment function basically does that, it reduces your html elements into react fragments that you can render.

React createFragment documentation

Alternatively, in a much better approach, you can create an AuthorLink stateless component like this..

function AuthorLink(props) {
  return (
    <div className="author-link">
      <span> by </span>
      <a href={props.authorUrl}> {props.author} </a>
    </div> 
  });
}

and use this in your main component's render

render() {
  const { author } = this.props;
  return (
    <div>
      {this.props.datePosted}
      <AuthorLink url={getAuthorUrl(author)} author={author} />
    </div>
  );
}

Upvotes: 0

Abdulrahman Alhamoudi
Abdulrahman Alhamoudi

Reputation: 16

Try this:

class Foo extends React.Component {
    _renderAuthor() {
        return <a href={getAuthorUrl(this.props.author)}>{this.props.author}</a>
    }

    render() {
        return (
          <div>
                {this.props.title}
                {this.props.author && " by "}
                {this.props.author && this._renderAuthor()}
          </div>
        );
    }
}

Upvotes: 0

Przemysław Zalewski
Przemysław Zalewski

Reputation: 3986

You can return fragments from sub-rendering functions but not from the main render function, at least before React 16. In order to do so, return an array of components. You don't need to set keys manually unless your fragment children will change (arrays are keyed with indices by default).

For creating fragments you may also use createFragment.

For inline usage, you may use an array or leverage immediately invoked arrow function. See the example below:

const getAuthorUrl = author => `/${author.toLowerCase()}`;

class Foo extends React.Component {
  constructor() {
     super();
     this._renderAuthor = this._renderAuthor.bind(this);
     this._renderUser = this._renderUser.bind(this);
  }
  
  _renderAuthor() {
    if (!this.props.author) {
      return null;
    }

    return [
      ' by ',
      <a href={getAuthorUrl(this.props.author)}>{this.props.author}</a>,
    ];
  }
  
  _renderUser() {
    return [
      <h2>{this.props.user.name}</h2>,
      <p>{this.props.user.info}</p>
    ]
  }
  
  render() {
    return (
      <div>
        {this.props.datePosted}
        {this._renderAuthor()}
        
        <div>
          {this.props.user
            ? this._renderUser()
            : <p>User not found</p>}
        </div>
        
        <div>
          {this.props.user
            ? [
                <h2>{this.props.user.name}</h2>,
                <p>{this.props.user.info}</p>
              ]
            : <p>User not found</p>}
        </div>
        
        <div>
          {this.props.user
            ? (() => [
                <h2>{this.props.user.name}</h2>,
                <p>{this.props.user.info}</p>
              ])()
            : <p>User not found</p>}
        </div>
      </div>
    );
  }
}

ReactDOM.render(<Foo datePosted="Today" author="Me" user={{name: 'test', info: 'info'}} />, document.getElementById('container'));
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>
<div id="container"></div>

In order to not get warnings each child must be assigned a key. In order to do so, instead of returning an array please use helper function fragment(...children) to assign index-based keys automatically. Please note that strings must be converted to spans or other nodes that can be assigned with a key:

const fragment = (...children) =>
    children.map((child, index) =>
        React.cloneElement(
            typeof child === 'string'
            ? <span>{child}</span>
            : child
        , { key: index }
        )
    )


const getAuthorUrl = author => `/${author.toLowerCase()}`;

const fragment = (...children) =>
    children.map((child, index) =>
        React.cloneElement(
            typeof child === 'string'
            ? <span>{child}</span>
            : child
        , { key: index }
        )
    )

class Foo extends React.Component {
  constructor() {
     super();
     this._renderAuthor = this._renderAuthor.bind(this);
     this._renderUser = this._renderUser.bind(this);
  }
  
  _renderAuthor() {
    if (!this.props.author) {
      return null;
    }

    return fragment(
      ' by ',
      <a href={getAuthorUrl(this.props.author)}>{this.props.author}</a>
    );
  }
  
  _renderUser() {
    return fragment(
      <h2>{this.props.user.name}</h2>,
      <p>{this.props.user.info}</p>
    )
  }
  
  render() {
    return (
      <div>
        {this.props.datePosted}
        {this._renderAuthor()}
        
        <div>
          {this.props.user
            ? this._renderUser()
            : <p>User not found</p>}
        </div>
        
        <div>
          {this.props.user
            ? fragment(
                <h2>{this.props.user.name}</h2>,
                <p>{this.props.user.info}</p>
              )
            : <p>User not found</p>}
        </div>
        
        <div>
          {this.props.user
            ? (() => fragment(
                <h2>{this.props.user.name}</h2>,
                <p>{this.props.user.info}</p>
              ))()
            : <p>User not found</p>}
        </div>
      </div>
    );
  }
}

ReactDOM.render(<Foo datePosted="Today" author="Me" user={{name: 'test', info: 'info'}} />, document.getElementById('container'));
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>
<div id="container"></div>

Upvotes: 0

Bruce Mu
Bruce Mu

Reputation: 893

There is another way to solve this. I will suggest you create another component Author.js:

function Author(props) {
  return (<span>
    <span> by </span>
    <a href={props.getAuthorUrl(props.author)}>{props.author}</a>
  </span>)
}


class Foo extends React.Component {
  render() {
    return (
      <div>
        {this.props.title}
        {this.props.author && <Author author={this.props.author} getAuthorUrl={this.getAuthorUrl} />}
      </div>
    );
  }
}

I didn't test this code though. But it will look more cleaner I think. Hope it helps.

Upvotes: 1

Daniel O Mensah
Daniel O Mensah

Reputation: 406

This is a bit hacky but it doesn't have unnecessary jsx as you wished.

var author = 'Daniel';
var title = 'Hello';

var Hello = React.createClass({
  _renderAutho0r: function() {
    if (!author) {
      return null;
    }

    return <a href="#">{author}</a>
},

    render: function() {
    var by = author ? ' by ' : null;

        return (
      <div>
        {title}
        {by}
        {this._renderAutho0r()}
      </div>
    );
    }
});

React.render(<Hello name="World" />, document.body);

my JSFiddle

Upvotes: 0

flq
flq

Reputation: 22849

I like to have an If-component around for such things, and I have wrapped everything into a span, as it doesn't really break anything and makes the need for keys go away...

const getAuthorUrl = author => `/${author.toLowerCase()}`;

function If({condition,children}) {
  return condition ? React.Children.only(children) : null;

}

class Foo extends React.Component {

  render() {
    return (
      <div>
        {this.props.datePosted}
        <If condition={this.props.author}>
          <span> by 
          <a key="author" href={getAuthorUrl(this.props.author)}>
            {this.props.author}
          </a>
          </span>
        </If>
      </div>
    );
  }
}

ReactDOM.render(<Foo datePosted="Today" author="Me"/>, document.getElementById('container'));
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>
<div id="container"></div>

...skipping the array thing altogether?

Upvotes: 0

Jordan Running
Jordan Running

Reputation: 106027

The error message tells you exactly how to solve this:

Each child in an array or iterator should have a unique "key" prop.

Instead of this:

return [
  ' by ',
  <a href={getAuthorUrl(this.props.author)}>{this.props.author}</a>,
];

Do this:

return [
  <span key="by"> by </span>,
  <a key="author" href={getAuthorUrl(this.props.author)}>{this.props.author}</a>,
];

Yes, you need to wrap the text node ("by") in a span in order to give it a key. Such are the breaks. As you can see, I've just given each element a static key, since there's nothing dynamic about them. You could just as well use key="1" and key="2" if you wanted.

Alternatively, you could do this:

return <span> by <a href={getAuthorUrl(this.props.author)}>{this.props.author}</a></span>;

...which obviates the need for keys.

Here's the former solution in a working snippet:

const getAuthorUrl = author => `/${author.toLowerCase()}`;

class Foo extends React.Component {
  _renderAuthor() {
    if (!this.props.author) {
      return null;
    }

    return [
      <span key="by"> by </span>,
      <a key="author" href={getAuthorUrl(this.props.author)}>{this.props.author}</a>,
    ];
  }

  render() {
    return (
      <div>
        {this.props.datePosted}
        {this._renderAuthor()}
      </div>
    );
  }
}

ReactDOM.render(<Foo datePosted="Today" author="Me"/>, document.getElementById('container'));
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>
<div id="container"></div>

Upvotes: 12

Robsonsjre
Robsonsjre

Reputation: 1606

Try this approach on your array:

return [
      <span key={'prefix-'+random_string_generator()}>' by '</span>,
      <a key={'prefix-'+random_string_generator()} href={getAuthorUrl(this.props.author)}>{this.props.author}</a>,
    ];

Upvotes: -4

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