packages/react/src/ReactChildren.js
/**
 * Returns the first child in a collection of children and verifies that there
 * is only one child in the collection.
 *
 * See https://reactjs.org/docs/react-api.html#reactchildrenonly
 *
 * The current implementation of this function assumes that a single child gets
 * passed without a wrapper, but the purpose of this helper function is to
 * abstract away the particular structure of children.
 *
 * @param {?object} children Child collection structure.
 * @return {ReactElement} The first and only `ReactElement` contained in the
 * structure.
 */
Returns the first child in a collection of children and verifies that there
is only one child in the collection.



The current implementation of this function assumes that a single child gets
passed without a wrapper, but the purpose of this helper function is to
abstract away the particular structure of children.

@param {?object} children Child collection structure.
@return {ReactElement} The first and only `ReactElement` contained in the
structure.
Returns the first child in a collection of children and verifies that there is only one child in the collection . The current implementation of this function assumes that a single child gets passed without a wrapper but the purpose of this helper function is to abstract away the particular structure of children . @param { ?object } children Child collection structure . @return { ReactElement } The first and only ` ReactElement ` contained in the structure .
function onlyChild(children) {
  invariant(
    isValidElement(children),
    'React.Children.only expected to receive a single React element child.',
  );
  return children;
}
function onlyChild ( children ) { invariant ( isValidElement ( children ) , 'React.Children.only expected to receive a single React element child.' , ) ; return children ; }
Returns the first child in a collection of children and verifies that there
 is only one child in the collection.
Returns the first child in a collection of children and verifies that there is only one child in the collection .