Reactソース読解-13_044

Reactソース読解-13React Element Function Object.getOwnPropertyDescriptor()メソッドは、指定されたオブジェクトの前の固有属性に対応する属性記述子を返すObject.defineProperty()メソッドは、オブジェクトに直接新しいプロパティを定義するか、オブジェクトの既存のプロパティを変更してオブジェクトに戻ります.hasValidRef
有効かどうかを判断するref

function hasValidRef(config) {
  if (__DEV__) {
    if (hasOwnProperty.call(config, 'ref')) {
      const getter = Object.getOwnPropertyDescriptor(config, 'ref').get;
      if (getter && getter.isReactWarning) {
        return false;
      }
    }
  }
  return config.ref !== undefined;
}

hasValidKey
有効かどうかを判断するKey

function hasValidKey(config) {
  if (__DEV__) {
    if (hasOwnProperty.call(config, 'key')) {
      const getter = Object.getOwnPropertyDescriptor(config, 'key').get;
      if (getter && getter.isReactWarning) {
        return false;
      }
    }
  }
  return config.key !== undefined;
}

https://developer.mozilla.org... defineKeyPropWarningGetter

function defineKeyPropWarningGetter(props, displayName) {
  const warnAboutAccessingKey = function() {
    if (!specialPropKeyWarningShown) {
      specialPropKeyWarningShown = true;
      warningWithoutStack(
        false,
        '%s: `key` is not a prop. Trying to access it will result ' +
          'in `undefined` being returned. If you need to access the same ' +
          'value within the child component, you should pass it as a different ' +
          'prop. (https://fb.me/react-special-props)',
        displayName,
      );
    }
  };
  warnAboutAccessingKey.isReactWarning = true;
  Object.defineProperty(props, 'key', {
    get: warnAboutAccessingKey,
    configurable: true,
  });
}

defineRefPropWarningGetter

function defineRefPropWarningGetter(props, displayName) {
  const warnAboutAccessingRef = function() {
    if (!specialPropRefWarningShown) {
      specialPropRefWarningShown = true;
      warningWithoutStack(
        false,
        '%s: `ref` is not a prop. Trying to access it will result ' +
          'in `undefined` being returned. If you need to access the same ' +
          'value within the child component, you should pass it as a different ' +
          'prop. (https://fb.me/react-special-props)',
        displayName,
      );
    }
  };
  warnAboutAccessingRef.isReactWarning = true;
  Object.defineProperty(props, 'ref', {
    get: warnAboutAccessingRef,
    configurable: true,
  });
}

ReactElement

  const ReactElement = function(type, key, ref, self, source, owner, props) {
  const element = {
    //                  React Element
    $$typeof: REACT_ELEMENT_TYPE,

    // Built-in properties that belong on the element
    type: type,
    key: key,
    ref: ref,
    props: props,

    //             。
    _owner: owner,
  };

  if (__DEV__) {
    //          。    
    //      ，            。
    //   WeakMap    ，     WeakMap
    //       。
    element._store = {};

    //      ReactElement     ，   
    //        （       ， 
    //                ），      
    //   。
    Object.defineProperty(element._store, 'validated', {
      configurable: false,
      enumerable: false,
      writable: true,
      value: false,
    });
    // self source  DEV   。
    Object.defineProperty(element, '_self', {
      configurable: false,
      enumerable: false,
      writable: false,
      value: self,
    });

    //                  
    //          ，              。
    Object.defineProperty(element, '_source', {
      configurable: false,
      enumerable: false,
      writable: false,
      value: source,
    });
    if (Object.freeze) {
      Object.freeze(element.props);
      Object.freeze(element);
    }
  }

  return element;
};

export function jsx

export function jsx(type, config, maybeKey) {
  let propName;

  // Reserved names are extracted
  const props = {};

  let key = null;
  let ref = null;

  //  ，key    props  。      
  //        key，      （ 

  // 
）。     key  ，
  //       ，          jsxDEV
  //
，            
  //key         。

  if (maybeKey !== undefined) {
    key = '' + maybeKey;
  }

  if (hasValidKey(config)) {
    key = '' + config.key;
  }

  if (hasValidRef(config)) {
    ref = config.ref;
  }

  // Remaining properties are added to a new props object
  for (propName in config) {
    if (
      hasOwnProperty.call(config, propName) &&
      !RESERVED_PROPS.hasOwnProperty(propName)
    ) {
      props[propName] = config[propName];
    }
  }

  // Resolve default props
  if (type && type.defaultProps) {
    const defaultProps = type.defaultProps;
    for (propName in defaultProps) {
      if (props[propName] === undefined) {
        props[propName] = defaultProps[propName];
      }
    }
  }

  return ReactElement(
    type,
    key,
    ref,
    undefined,
    undefined,
    ReactCurrentOwner.current,
    props,
  );
}

jsxDev

行为几乎和 jsx 一致,主要就是defineKeyPropWarningGetter和defineRefPropWarningGetter的处理

createElement

创建并返回指定类型的新 React 元素。

export function createElement(type, config, children) {
  let propName;

  // Reserved names are extracted
  const props = {};

  let key = null;
  let ref = null;
  let self = null;
  let source = null;

  if (config != null) {
    if (hasValidRef(config)) {
      ref = config.ref;
    }
    if (hasValidKey(config)) {
      key = '' + config.key;
    }

    self = config.__self === undefined ? null : config.__self;
    source = config.__source === undefined ? null : config.__source;
    // Remaining properties are added to a new props object
    for (propName in config) {
      if (
        hasOwnProperty.call(config, propName) &&
        !RESERVED_PROPS.hasOwnProperty(propName)
      ) {
        props[propName] = config[propName];
      }
    }
  }

  // Children can be more than one argument, and those are transferred onto
  // the newly allocated props object.
  const childrenLength = arguments.length - 2;
  if (childrenLength === 1) {
    props.children = children;
  } else if (childrenLength > 1) {
    const childArray = Array(childrenLength);
    for (let i = 0; i < childrenLength; i++) {
      childArray[i] = arguments[i + 2];
    }
    if (__DEV__) {
      if (Object.freeze) {
        Object.freeze(childArray);
      }
    }
    props.children = childArray;
  }

  // Resolve default props
  if (type && type.defaultProps) {
    const defaultProps = type.defaultProps;
    for (propName in defaultProps) {
      if (props[propName] === undefined) {
        props[propName] = defaultProps[propName];
      }
    }
  }
  if (__DEV__) {
    if (key || ref) {
      const displayName =
        typeof type === 'function'
          ? type.displayName || type.name || 'Unknown'
          : type;
      if (key) {
        defineKeyPropWarningGetter(props, displayName);
      }
      if (ref) {
        defineRefPropWarningGetter(props, displayName);
      }
    }
  }
  return ReactElement(
    type,
    key,
    ref,
    self,
    source,
    ReactCurrentOwner.current,
    props,
  );
}

createFactory
この補助関数は破棄されました

export function createFactory(type) {
  const factory = createElement.bind(null, type);
  //           ，    
  //       。  。 `.type === Foo`。
  //       “ constructor”，         
  //     ，          。
  //    ：    
  factory.type = type;
  return factory;
}

cloneElement element要素をテンプレートとしてクローンし、新しいReact要素を返します.戻り要素のpropsは、新しいpropsを元の要素のpropsの浅い層と結合した結果である.新しいサブエレメントは既存のサブエレメントに取って代わり、元のエレメントからのkeyおよびrefが保持されます.isValidElement
オブジェクトがReact要素であるかどうかを確認します.戻り値はtrueまたはfalseです.

export function isValidElement(object) {
  // typeof null = object
  return (
    typeof object === 'object' &&
    object !== null &&
    object.$$typeof === REACT_ELEMENT_TYPE
  );
}

https://zh-hans.reactjs.org/d...