Why do I get the error "expressions must have one parent element", how do I fix this?

I'm relatively new to React and I'm wondering what's the standard here.

Imagine I have a react-router like this one:

<Router history={history}>
    <Route path="/" component={App}>
      <Route path="home component={Home} />
      <Route path="about" component={About} />
      <Route path="inbox" component={Inbox} />
      <Route path="contacts" component={Contacts} />
    </Route>
</Router>

And now I want to remove two routes if prop.mail is set to false, so a sane way of doing that would look like this:

<Router history={history}>
      <Route path="/" component={App}>
        <Route path="home component={Home} />
        <Route path="about" component={About} />
        
        { if.this.props.mail ? 
          <Route path="inbox" component={Inbox} />
          <Route path="contacts" component={Contacts} />
        : null }
 
      </Route>
 </Router>

But there are 2 routes and React returns error:

> expressions must have one parent element.

I don't want to use multiple ifs here. What's the preferred React way of handling this?

Put them in an array (assign the keys also):

{ if.this.props.mail ? 
    [
        <Route key={0} path="inbox" component={Inbox} />,
        <Route key={1} path="contacts" component={Contacts} />
    ]
: null }

With latest React version, you can try React.Fragment also, like this:

{ if.this.props.mail ? 
    <React.Fragment>
        <Route path="inbox" component={Inbox} />,
        <Route path="contacts" component={Contacts} />
    </React.Fragment>
: null }

You can leverage short hand fragments to return a list of children along with Logical '&&' Operator for conditional rendering. Nice and clean! 

{this.props.mail && 
  <>
    <Route path="inbox" component={Inbox} />,
    <Route path="contacts" component={Contacts} />
  </>
}

You must been use a fragment tag e.g(div, <>,...).

Check this short solution:

{ if.this.props.mail ? 
 <>
   <Route path="inbox" component={Inbox} />
   <Route path="contacts" component={Contacts} />
 </>
 : null }

just try enclosing the code after the return statement in an element like <div>....code </div>,etc.

eg:-

const Div =()=>{
           return
            <div>
              <Button name="Save" ></Button>
              <Button name="Edit"></Button>
              <Button name="Cancel"></Button>  
            </div>}

2020 update

I have checked out every solution from answers. Here is the breakdown for regular React:

1. React Fragment

When i wanted to use it once, without adding additional DOM node - it worked. When i tried to use second React.Fragment got really bad errors. Wasn't able to fix it.

2. View

I was unable to import View properly. I don't know if this is only for Reactjs, or Native, but this does not work

3. Div

What actually worked was to put HTML into Div

Faced the same error in a similar situation (React Native).

export default class App extends React.Component {
  render() {
    return (
      <StatusBar barStyle="default" />
      <AppContainer />
    );
  }
}

As indicated in the error prompt the JSX expression requires to have one parent element, hence wrap the elements in the return expression with a parent element. The flex: 1 style was added to allow the <View> element assume the height of the entire screen.

export default class App extends React.Component {
  render() {
    return (
      <View style={{flex: 1}}>
        <StatusBar barStyle="default" />
        <AppContainer />
      </View>
    );
  }
}

This one works for me.

……..

If you're using <Switch>, then using <div> and <React.Fragment> to wrap your routes will break it.

I like the idea of a <ProtectedRoute> component:

import { Component } from 'react';
import { Redirect, Route } from 'react-router-dom';

class ProtectedRoute extends Component<any> {
  render() {
    const { component: Component, allow, ...props } = this.props;
    if (!allow) {
      return <Redirect to={{ pathname: '/signin' }} />;
    }
    return <Route {...props} render={(props) => <Component {...props} />} />;
  }
}

export default ProtectedRoute;

Then use it like below:

<Router history={history}>
  <Route path="/" component={App}>
    <Route path="home" component={Home} />
    <Route path="about" component={About} />

    <ProtectedRoute path="inbox" component={Inbox} allow={this.props.mail} />
    <ProtectedRoute path="contacts" component={Contacts} allow={this.props.mail} />

  </Route>
</Router>