[Proposal] Selective Render with useContext

[eduardocque]

Ability to do selective renders with useContext to improve the performance for large applications

following the next pattern

const TestContext = createContext();
...
const proposalCallback = useCallback(
    (prevState, nextState) => {
      // If the value is different, then re-render
      // if this method is defined will return true/false
      // if this method doesn't exist, will keeps working in the current way re-rendering everytime so this one is optional


      return "evaluate prev and next state and based on your logic return true or false";
    },
    []
  );

  // Proposal callback applied here
  const dataContext = useContext(TestContext, proposalCallback);

React version: 18.2.0

Steps To Reproduce

• open console log
• write in the first field and u will notice that field 2 is re-rendering, we should skip it

https://codesandbox.io/s/friendly-bas-5vnrvs

The current behavior

all context consumers are re-rendering

The expected behavior

should only re-render those that were affected using the proposal that is in codesandbox

Note

this proposal is to give a big improvement in performance for large application that works based on contexts, so instead be making granual contexts, why not give the ability to check if the value that is expecting the consumer change or not

this can be implemented in the logic that process the nodes and takes the decision to re-render or not internally in react, but im not familiar to try to make a PR for this proposal

Updated:

after some research the files that needs to be updated are

• packages/react-reconciler/src/ReactFiberNewContext.js -> propagateContextChange

is this correct ?

noticed that when the provider Fiber gets updated this sends the signal to invalidate all consumers located in the child tree inside the provider

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