(React) Type '() => JSX.Element[]' is not assignable to type FunctionComponent

# (React) Type '() => JSX.Element[]' is not assignable to type FunctionComponent

The React.js error "Type '() => JSX.Element[]' is not assignable to type FunctionComponent" occurs when we try to return an array of elements from a function component.

To solve the error, wrap the array of elements into a React fragment.

Here is an example of how the error occurs.

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import React from 'react';

// ⛔️ Type '() => JSX.Element[]' is not assignable to type 'FunctionComponent<{}>'.
// Type 'Element[]' is missing the following properties
// from type 'ReactElement<any, any>': type, props, key ts(2322)

const App: React.FunctionComponent = () => {
  return ['Alice', 'Bob'].map(element => <div key={element}>{element}</div>);
};

export default App;

This is perfectly valid React.js code as we should be able to return an array from a function component in React.

However, the return type of the FunctionComponent interface is ReactElement or null.

Therefore we can only return a React element or a null value.

# Wrap the array in a React fragment

To get around the type error, we have to wrap the array in a React fragment.

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import React from 'react';

const App: React.FunctionComponent = () => {
  return (
    <>
      {['Alice', 'Bob'].map(element => (
        <div key={element}>{element}</div>
      ))}
    </>
  );
};

export default App;

Fragments are used when we need to group a list of elements without adding extra nodes to the DOM.

You might also see the more verbose syntax of fragments being used.

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import React from 'react';

const App: React.FunctionComponent = () => {
  return (
    <React.Fragment>
      {['Alice', 'Bob'].map(element => (
        <div key={element}>{element}</div>
      ))}
    </React.Fragment>
  );
};

export default App;

The two examples above achieve the same result - they group the list of elements elements without adding extra nodes to the DOM.

# Wrap the array in another DOM element

An alternative solution is to wrap the array of elements in another DOM element, e.g. a div.

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import React from 'react';

const App: React.FunctionComponent = () => {
  return (
    <div>
      {['Alice', 'Bob'].map(element => (
        <div key={element}>{element}</div>
      ))}
    </div>
  );
};

export default App;

This still conforms to the specified in the FunctionComponent interface return type, because our component returns a single React element.