Function createElement

packages/react/src/jsx/ReactJSXElement.js:560–684

(type, config, children)

 * See https://reactjs.org/docs/react-api.html#createelement
 */
export function createElement(type, config, children) {
  if (__DEV__) {
    // We don't warn for invalid element type here because with owner stacks,
    // we error in the renderer. The renderer is the only one that knows what
    // types are valid for this particular renderer so we let it error there.

    // Skip key warning if the type isn't valid since our key validation logic
    // doesn't expect a non-string/function type and can throw confusing
    // errors. We don't want exception behavior to differ between dev and
    // prod. (Rendering will throw with a helpful message and as soon as the
    // type is fixed, the key warnings will appear.)
    for (let i = 2; i < arguments.length; i++) {
      validateChildKeys(arguments[i]);
    }

    // Unlike the jsx() runtime, createElement() doesn't warn about key spread.
  }

  let propName;

  // Reserved names are extracted
  const props = {};

  let key = null;

  if (config != null) {
    if (__DEV__) {
      if (
        !didWarnAboutOldJSXRuntime &&
        '__self' in config &&
        // Do not assume this is the result of an oudated JSX transform if key
        // is present, because the modern JSX transform sometimes outputs
        // createElement to preserve precedence between a static key and a
        // spread key. To avoid false positive warnings, we never warn if
        // there's a key.
        !('key' in config)
      ) {
        didWarnAboutOldJSXRuntime = true;
        console.warn(
          'Your app (or one of its dependencies) is using an outdated JSX ' +
            'transform. Update to the modern JSX transform for ' +
            'faster performance: https://react.dev/link/new-jsx-transform',
        );
      }
    }

    if (hasValidKey(config)) {
      if (__DEV__) {
        checkKeyStringCoercion(config.key);
      }
      key = '' + config.key;
    }

    // Remaining properties are added to a new props object
    for (propName in config) {
      if (
        hasOwnProperty.call(config, propName) &&
        // Skip over reserved prop names