Function createChild

packages/react-reconciler/src/ReactChildFiber.js:681–809

(
    returnFiber: Fiber,
    newChild: any,
    lanes: Lanes,
  )

  }

  function createChild(
    returnFiber: Fiber,
    newChild: any,
    lanes: Lanes,
  ): Fiber | null {
    if (
      (typeof newChild === 'string' && newChild !== '') ||
      typeof newChild === 'number' ||
      typeof newChild === 'bigint'
    ) {
      // Text nodes don't have keys. If the previous node is implicitly keyed
      // we can continue to replace it without aborting even if it is not a text
      // node.
      const created = createFiberFromText(
        // $FlowFixMe[unsafe-addition] Flow doesn't want us to use `+` operator with string and bigint
        '' + newChild,
        returnFiber.mode,
        lanes,
      );
      created.return = returnFiber;
      if (__DEV__) {
        // We treat the parent as the owner for stack purposes.
        created._debugOwner = returnFiber;
        created._debugTask = returnFiber._debugTask;
        created._debugInfo = currentDebugInfo;
      }
      return created;
    }

    if (typeof newChild === 'object' && newChild !== null) {
      switch (newChild.$$typeof) {
        case REACT_ELEMENT_TYPE: {
          const created = createFiberFromElement(
            newChild,
            returnFiber.mode,
            lanes,
          );
          coerceRef(created, newChild);
          created.return = returnFiber;
          if (__DEV__) {
            const prevDebugInfo = pushDebugInfo(newChild._debugInfo);
            created._debugInfo = currentDebugInfo;
            currentDebugInfo = prevDebugInfo;
          }
          return created;
        }
        case REACT_PORTAL_TYPE: {
          const created = createFiberFromPortal(
            newChild,
            returnFiber.mode,
            lanes,
          );
          created.return = returnFiber;
          if (__DEV__) {
            created._debugInfo = currentDebugInfo;
          }
          return created;
        }