Appendix

Appendix A – Propagating a context

React comes with different kinds of fibers. While a function component is one of them, the context provider is another one. It gets its own update logic with each update:

function updateContextProvider(fiber) {
  var providerType = fiber.type
  var context = providerType._context
  var newProps = fiber.pendingProps
  var oldProps = fiber.memoizedProps
  var newValue = newProps.value
  if (oldProps !== null) { ... }
  var children = newProps.children
  reconcileChildren(fiber, children)
  return fiber.child
}

In the preceding code, the updateContextProvider function takes in fiber, and checks whether it has been mounted or not via oldProps !== null. If it's a first-time mount, then it does things similar to a function component, reconciling the children into fibers and then returning the first child to work on next.

If it&apos...