React 궁금증

1. useEffect 사용시 의존성 배열에 따라서 다른 console.log를 찍고 싶다면 ?

  useEffect(() => {
    console.log("렌더링이 완료되었습니다 ");
    // console.log({ names });
    if (names.includes("안녕")) {
      console.log("반갑습니다");
    }
    return () => {
      console.log("clean up");
      console.log({ names });
    };
  }, [names, text]);

-의존성 배열에 넣은 값을 기준으로 조건문을 넣으면 의존성 배열값이 바뀔때마다 바뀐 값에 따라 다른 값을 얻을 수 있다.

2. useState와 useRef를 어떻게 구분해서 사용하는 것이 현명할까 ?

useState는 값이 변경될 때마다 렌더링이 되고
useRef는 값이 변경되어도 렌더링이 되지 않아서 보여지는 값도 바뀌지 않는다
➡️ useState는 실시간으로 값이 변경되는 것이 '화면'에서 보여져야 한다면 사용
- useRef는 값이 최종적으로 한번에 일괄적으로 바뀌니깐 input에 값을 다 입력받고 한 번에 값을 넘겨주는 경우 등에 사용하면 좋지 않을까


3. context
context 사용하다 그냥 안에 어떻게 생겼는지 궁금해서 콘솔에 찍어보니
아래와 같은 결과가 나와서 단순 기록용으로 코드 남김

function useContext(Context) {
  var dispatcher = resolveDispatcher();

  {
    // TODO: add a more generic warning for invalid values.
    if (Context._context !== undefined) {
      var realContext = Context._context; // Don't deduplicate because this legitimately causes bugs
      // and nobody should be using this in existing code.

      if (realContext.Consumer === Context) {
        error('Calling useContext(Context.Consumer) is not supported, may cause bugs, and will be ' + 'removed in a future major release. Did you mean to call useContext(Context) instead?');
      } else if (realContext.Provider === Context) {
        error('Calling useContext(Context.Provider) is not supported. ' + 'Did you mean to call useContext(Context) instead?');
      }
    }
  }

  return dispatcher.useContext(Context);
}

function createContext(defaultValue) {
  // TODO: Second argument used to be an optional `calculateChangedBits`
  // function. Warn to reserve for future use?
  var context = {
    $$typeof: REACT_CONTEXT_TYPE,
    // As a workaround to support multiple concurrent renderers, we categorize
    // some renderers as primary and others as secondary. We only expect
    // there to be two concurrent renderers at most: React Native (primary) and
    // Fabric (secondary); React DOM (primary) and React ART (secondary).
    // Secondary renderers store their context values on separate fields.
    _currentValue: defaultValue,
    _currentValue2: defaultValue,
    // Used to track how many concurrent renderers this context currently
    // supports within in a single renderer. Such as parallel server rendering.
    _threadCount: 0,
    // These are circular
    Provider: null,
    Consumer: null,
    // Add these to use same hidden class in VM as ServerContext
    _defaultValue: null,
    _globalName: null
  };
  context.Provider = {
    $$typeof: REACT_PROVIDER_TYPE,
    _context: context
  };
  var hasWarnedAboutUsingNestedContextConsumers = false;
  var hasWarnedAboutUsingConsumerProvider = false;
  var hasWarnedAboutDisplayNameOnConsumer = false;

  {
    // A separate object, but proxies back to the original context object for
    // backwards compatibility. It has a different $$typeof, so we can properly
    // warn for the incorrect usage of Context as a Consumer.
    var Consumer = {
      $$typeof: REACT_CONTEXT_TYPE,
      _context: context
    }; // $FlowFixMe: Flow complains about not setting a value, which is intentional here

    Object.defineProperties(Consumer, {
      Provider: {
        get: function () {
          if (!hasWarnedAboutUsingConsumerProvider) {
            hasWarnedAboutUsingConsumerProvider = true;

            error('Rendering <Context.Consumer.Provider> is not supported and will be removed in ' + 'a future major release. Did you mean to render <Context.Provider> instead?');
          }

          return context.Provider;
        },
        set: function (_Provider) {
          context.Provider = _Provider;
        }
      },
      _currentValue: {
        get: function () {
          return context._currentValue;
        },
        set: function (_currentValue) {
          context._currentValue = _currentValue;
        }
      },
      _currentValue2: {
        get: function () {
          return context._currentValue2;
        },
        set: function (_currentValue2) {
          context._currentValue2 = _currentValue2;
        }
      },
      _threadCount: {
        get: function () {
          return context._threadCount;
        },
        set: function (_threadCount) {
          context._threadCount = _threadCount;
        }
      },
      Consumer: {
        get: function () {
          if (!hasWarnedAboutUsingNestedContextConsumers) {
            hasWarnedAboutUsingNestedContextConsumers = true;

            error('Rendering <Context.Consumer.Consumer> is not supported and will be removed in ' + 'a future major release. Did you mean to render <Context.Consumer> instead?');
          }

          return context.Consumer;
        }
      },
      displayName: {
        get: function () {
          return context.displayName;
        },
        set: function (displayName) {
          if (!hasWarnedAboutDisplayNameOnConsumer) {
            warn('Setting `displayName` on Context.Consumer has no effect. ' + "You should set it directly on the context with Context.displayName = '%s'.", displayName);

            hasWarnedAboutDisplayNameOnConsumer = true;
          }
        }
      }
    }); // $FlowFixMe: Flow complains about missing properties because it doesn't understand defineProperty

    context.Consumer = Consumer;
  }

  {
    context._currentRenderer = null;
    context._currentRenderer2 = null;
  }

  return context;
}