ReactElement

/**
 * 生成react元素的工厂方法，不再采用类模式，因此不能使用new调用
 * 不支持instanceof检测类型
 * 而只能通过$$typeof ===   Symbol.for('react.element')判断是否是react元素
 */
const ReactElement = function(type, key, ref, self, source, owner, props) {
  const element = {
    // react元素标识，REACT_ELEMENT_TYPE = hasSymbol? Symbol.for('react.element'): 0xeac7;
    $$typeof: REACT_ELEMENT_TYPE,

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

    // Record the component responsible for creating this element.
    _owner: owner,
  };
  return element;
};

jsx方法

/**
 * @param {*} type
 * @param {object} props
 * @param {string} key
 */
export function jsx(type, config, maybeKey) {
  // 属性名，避免重复声明
  let propName;

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

  let key = null;
  let ref = null;

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

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

  // 将config中包含的属性（除key，ref，__self，__source）浅拷贝到props对象中
  for (propName in config) {
    if (
    /* const RESERVED_PROPS = {
     * key: true,
     * ref: true,
     * __self: true,
     * __source: true, 
     */
      hasOwnProperty.call(config, propName) &&
      !RESERVED_PROPS.hasOwnProperty(propName)
    ) {
      props[propName] = config[propName];
    }
  }

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

  // 设置默认属性
  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,
  );
}

createElement

实现代码多处和jsx相同

/**
 * Create and return a new ReactElement of the given type.
 * See https://reactjs.org/docs/react-api.html#createelement
 */
export function createElement(type, config, children) {
  let propName;

  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];
      }
    }
  }

  // 多于三个参数都被默认认定是children
  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;
  }

  // 默认属性
  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,
    self,
    source,
    ReactCurrentOwner.current,
    props,
  );
}

createFactory

生成type类型的react元素。 官网上说这是遗留下来的方法，目前鼓励使用jsx方法或者直接使用createElement方法。

export function createFactory(type) {
  const factory = createElement.bind(null, type);
  // 直接暴露类型，使得`<Foo />.type === Foo`
  factory.type = type;
  return factory;
}

cloneAndReplaceKey

使用新的key克隆react对象，搜索后发现在源码ReactChildren中有使用。

export function cloneAndReplaceKey(oldElement, newKey) {
  const newElement = ReactElement(
    oldElement.type,
    newKey,
    oldElement.ref,
    oldElement._self,
    oldElement._source,
    oldElement._owner,
    oldElement.props,
  );

  return newElement;
}

cloneElement

export function cloneElement(element, config, children) {
  // element不能为null或undefined，否则报错
  invariant(
    !(element === null || element === undefined),
    'React.cloneElement(...): The argument must be a React element, but you passed %s.',
    element,
  );

  let propName;

  // 复制要复制react元素的属性值
  const props = Object.assign({}, element.props);

  let key = element.key;
  let ref = element.ref;

  const self = element._self;

  const source = element._source;

  let owner = element._owner;

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

    // 默认属性
    let defaultProps;
    if (element.type && element.type.defaultProps) {
      defaultProps = element.type.defaultProps;
    }
    // 添加新增属性
    for (propName in config) {
      if (
        hasOwnProperty.call(config, propName) &&
        !RESERVED_PROPS.hasOwnProperty(propName)
      ) {
        if (config[propName] === undefined && defaultProps !== undefined) {
          // Resolve default props
          props[propName] = defaultProps[propName];
        } else {
          props[propName] = config[propName];
        }
      }
    }
  }

  // 参数多于三个都被认为是children
  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];
    }
    props.children = childArray;
  }

  return ReactElement(element.type, key, ref, self, source, owner, props);
}

isValidElement

判断是否是react元素

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