Function jsxDEVImpl

packages/react/src/jsx/ReactJSXElement.js:427–554

(
  type,
  config,
  maybeKey,
  isStaticChildren,
  debugStack,
  debugTask,
)

}

function jsxDEVImpl(
  type,
  config,
  maybeKey,
  isStaticChildren,
  debugStack,
  debugTask,
) {
  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.)
    // With owner stacks, we no longer need the type here so this comment is
    // no longer true. Which is why we can run this even for invalid types.
    const children = config.children;
    if (children !== undefined) {
      if (isStaticChildren) {
        if (isArray(children)) {
          for (let i = 0; i < children.length; i++) {
            validateChildKeys(children[i]);
          }

          if (Object.freeze) {
            Object.freeze(children);
          }
        } else {
          console.error(
            'React.jsx: Static children should always be an array. ' +
              'You are likely explicitly calling React.jsxs or React.jsxDEV. ' +
              'Use the Babel transform instead.',
          );
        }
      } else {
        validateChildKeys(children);
      }
    }

    // Warn about key spread regardless of whether the type is valid.
    if (hasOwnProperty.call(config, 'key')) {
      const componentName = getComponentNameFromType(type);
      const keys = Object.keys(config).filter(k => k !== 'key');
      const beforeExample =
        keys.length > 0
          ? '{key: someKey, ' + keys.join(': ..., ') + ': ...}'
          : '{key: someKey}';
      if (!didWarnAboutKeySpread[componentName + beforeExample]) {
        const afterExample =
          keys.length > 0 ? '{' + keys.join(': ..., ') + ': ...}' : '{}';
        console.error(
          'A props object containing a "key" prop is being spread into JSX:\n' +
            '  let props = %s;\n' +
            '  <%s {...props} />\n' +