小前端读源码 - React16.7.0(三)

import React from 'react';
import ReactDOM from 'react-dom';

class H1 extends React.Component {
    static defaultProps = {
        text: 'DEMO'
    }
    render() {
        return (<h1>{this.props.text}</h1>)
    }
}

class App extends React.Component {

    
    render() {
        return (<H1/>)
    }
}

ReactDOM.render(
    <App/>,
    document.getElementById('root'),
    () => {
        console.log(1, arguments);
    }
)

// This is used to create an alternate fiber to do work on.
function createWorkInProgress(current, pendingProps, expirationTime) {
  var workInProgress = current.alternate;
  if (workInProgress === null) {
    // We use a double buffering pooling technique because we know that we'll
    // only ever need at most two versions of a tree. We pool the "other" unused
    // node that we're free to reuse. This is lazily created to avoid allocating
    // extra objects for things that are never updated. It also allow us to
    // reclaim the extra memory if needed.
    workInProgress = createFiber(current.tag, pendingProps, current.key, current.mode);
    workInProgress.elementType = current.elementType;
    workInProgress.type = current.type;
    workInProgress.stateNode = current.stateNode;

    {
      // DEV-only fields
      workInProgress._debugID = current._debugID;
      workInProgress._debugSource = current._debugSource;
      workInProgress._debugOwner = current._debugOwner;
    }

    workInProgress.alternate = current;
    current.alternate = workInProgress;
  } else {
    workInProgress.pendingProps = pendingProps;

    // We already have an alternate.
    // Reset the effect tag.
    workInProgress.effectTag = NoEffect;

    // The effect list is no longer valid.
    workInProgress.nextEffect = null;
    workInProgress.firstEffect = null;
    workInProgress.lastEffect = null;

    if (enableProfilerTimer) {
      // We intentionally reset, rather than copy, actualDuration & actualStartTime.
      // This prevents time from endlessly accumulating in new commits.
      // This has the downside of resetting values for different priority renders,
      // But works for yielding (the common case) and should support resuming.
      workInProgress.actualDuration = 0;
      workInProgress.actualStartTime = -1;
    }
  }

  workInProgress.childExpirationTime = current.childExpirationTime;
  workInProgress.expirationTime = current.expirationTime;

  workInProgress.child = current.child;
  workInProgress.memoizedProps = current.memoizedProps;
  workInProgress.memoizedState = current.memoizedState;
  workInProgress.updateQueue = current.updateQueue;
  workInProgress.firstContextDependency = current.firstContextDependency;

  // These will be overridden during the parent's reconciliation
  workInProgress.sibling = current.sibling;
  workInProgress.index = current.index;
  workInProgress.ref = current.ref;

  if (enableProfilerTimer) {
    workInProgress.selfBaseDuration = current.selfBaseDuration;
    workInProgress.treeBaseDuration = current.treeBaseDuration;
  }

  return workInProgress;
}

function workLoop(isYieldy) {
  if (!isYieldy) {
    // Flush work without yielding
    while (nextUnitOfWork !== null) {
      nextUnitOfWork = performUnitOfWork(nextUnitOfWork);
    }
  } else {
    // Flush asynchronous work until there's a higher priority event
    while (nextUnitOfWork !== null && !shouldYieldToRenderer()) {
      nextUnitOfWork = performUnitOfWork(nextUnitOfWork);
    }
  }
}

function updateHostRoot(current$$1, workInProgress, renderExpirationTime) {
  pushHostRootContext(workInProgress);
  var updateQueue = workInProgress.updateQueue;
  !(updateQueue !== null) ? invariant(false, 'If the root does not have an updateQueue, we should have already bailed out. This error is likely caused by a bug in React. Please file an issue.') : void 0;
  var nextProps = workInProgress.pendingProps;
  var prevState = workInProgress.memoizedState;
  var prevChildren = prevState !== null ? prevState.element : null;
  // 设置workInProgress.memoizedState
  processUpdateQueue(workInProgress, updateQueue, nextProps, null, renderExpirationTime);
  var nextState = workInProgress.memoizedState;
  // Caution: React DevTools currently depends on this property
  // being called "element".
  var nextChildren = nextState.element;
  if (nextChildren === prevChildren) {
    // If the state is the same as before, that's a bailout because we had
    // no work that expires at this time.
    resetHydrationState();
    return bailoutOnAlreadyFinishedWork(current$$1, workInProgress, renderExpirationTime);
  }
  var root = workInProgress.stateNode;
  if ((current$$1 === null || current$$1.child === null) && root.hydrate && enterHydrationState(workInProgress)) {
    // If we don't have any current children this might be the first pass.
    // We always try to hydrate. If this isn't a hydration pass there won't
    // be any children to hydrate which is effectively the same thing as
    // not hydrating.

    // This is a bit of a hack. We track the host root as a placement to
    // know that we're currently in a mounting state. That way isMounted
    // works as expected. We must reset this before committing.
    // TODO: Delete this when we delete isMounted and findDOMNode.
    workInProgress.effectTag |= Placement;

    // Ensure that children mount into this root without tracking
    // side-effects. This ensures that we don't store Placement effects on
    // nodes that will be hydrated.
    workInProgress.child = mountChildFibers(workInProgress, null, nextChildren, renderExpirationTime);
  } else {
    // Otherwise reset hydration state in case we aborted and resumed another
    // root.
    reconcileChildren(current$$1, workInProgress, nextChildren, renderExpirationTime);
    resetHydrationState();
  }
  return workInProgress.child;
}

function reconcileChildren(current$$1, workInProgress, nextChildren, renderExpirationTime) {
  if (current$$1 === null) {
    // If this is a fresh new component that hasn't been rendered yet, we
    // won't update its child set by applying minimal side-effects. Instead,
    // we will add them all to the child before it gets rendered. That means
    // we can optimize this reconciliation pass by not tracking side-effects.
    workInProgress.child = mountChildFibers(workInProgress, null, nextChildren, renderExpirationTime);
  } else {
    // 进入这里
    // If the current child is the same as the work in progress, it means that
    // we haven't yet started any work on these children. Therefore, we use
    // the clone algorithm to create a copy of all the current children.

    // If we had any progressed work already, that is invalid at this point so
    // let's throw it out.
    workInProgress.child = reconcileChildFibers(workInProgress, current$$1.child, nextChildren, renderExpirationTime);
  }
}

// This API will tag the children with the side-effect of the reconciliation
  // itself. They will be added to the side-effect list as we pass through the
  // children and the parent.
  function reconcileChildFibers(returnFiber, currentFirstChild, newChild, expirationTime) {
    // This function is not recursive.
    // If the top level item is an array, we treat it as a set of children,
    // not as a fragment. Nested arrays on the other hand will be treated as
    // fragment nodes. Recursion happens at the normal flow.

    // Handle top level unkeyed fragments as if they were arrays.
    // This leads to an ambiguity between <>{[...]}</> and <>...</>.
    // We treat the ambiguous cases above the same.
    var isUnkeyedTopLevelFragment = typeof newChild === 'object' && newChild !== null && newChild.type === REACT_FRAGMENT_TYPE && newChild.key === null;
    if (isUnkeyedTopLevelFragment) {
      newChild = newChild.props.children;
    }

    // Handle object types
    var isObject = typeof newChild === 'object' && newChild !== null;

    if (isObject) {
      switch (newChild.$$typeof) {
        case REACT_ELEMENT_TYPE:
          return placeSingleChild(reconcileSingleElement(returnFiber, currentFirstChild, newChild, expirationTime));
        case REACT_PORTAL_TYPE:
          return placeSingleChild(reconcileSinglePortal(returnFiber, currentFirstChild, newChild, expirationTime));
      }
    }

    if (typeof newChild === 'string' || typeof newChild === 'number') {
      return placeSingleChild(reconcileSingleTextNode(returnFiber, currentFirstChild, '' + newChild, expirationTime));
    }

    if (isArray(newChild)) {
      return reconcileChildrenArray(returnFiber, currentFirstChild, newChild, expirationTime);
    }

    if (getIteratorFn(newChild)) {
      return reconcileChildrenIterator(returnFiber, currentFirstChild, newChild, expirationTime);
    }

    if (isObject) {
      throwOnInvalidObjectType(returnFiber, newChild);
    }

    {
      if (typeof newChild === 'function') {
        warnOnFunctionType();
      }
    }
    if (typeof newChild === 'undefined' && !isUnkeyedTopLevelFragment) {
      // If the new child is undefined, and the return fiber is a composite
      // component, throw an error. If Fiber return types are disabled,
      // we already threw above.
      switch (returnFiber.tag) {
        case ClassComponent:
          {
            {
              var instance = returnFiber.stateNode;
              if (instance.render._isMockFunction) {
                // We allow auto-mocks to proceed as if they're returning null.
                break;
              }
            }
          }
        // Intentionally fall through to the next case, which handles both
        // functions and classes
        // eslint-disable-next-lined no-fallthrough
        case FunctionComponent:
          {
            var Component = returnFiber.type;
            invariant(false, '%s(...): Nothing was returned from render. This usually means a return statement is missing. Or, to render nothing, return null.', Component.displayName || Component.name || 'Component');
          }
      }
    }

    // Remaining cases are all treated as empty.
    return deleteRemainingChildren(returnFiber, currentFirstChild);
  }

  return reconcileChildFibers;
}