babel如何解析jsx

<div className='box'>
  <h1 className='title' style={{'color':'red'}}>React源码解析</h1>
  <ul>
    <li>第一章</li>
    <li>第二章</li>
    <li>第三章</li>
    <li>第四章</li>
  </ul>
</div>

// packages/react/src/jsx/ReactJSX.js
import {REACT_FRAGMENT_TYPE} from 'shared/ReactSymbols';
import {
  jsxWithValidationStatic,
  jsxWithValidationDynamic,
  jsxWithValidation,
} from './ReactJSXElementValidator';
import {jsx as jsxProd} from './ReactJSXElement';
const jsx = __DEV__ ? jsxWithValidationDynamic : jsxProd;
const jsxs = __DEV__ ? jsxWithValidationStatic : jsxProd;
const jsxDEV = __DEV__ ? jsxWithValidation : undefined;

export {REACT_FRAGMENT_TYPE as Fragment, jsx, jsxs, jsxDEV};

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

  //标签上的属性集合
  const props = {};

  //单独处理key ref
  let key = null;
  let ref = null;

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

  if (hasValidKey(config)) {
    // 处理合法的key
    key = '' + config.key;
  }

  if (hasValidRef(config)) {
    // 处理合法的ref
    ref = config.ref;
  }

  // 把属性加到props中
  for (propName in config) {
    if (
      hasOwnProperty.call(config, propName) &&
      !RESERVED_PROPS.hasOwnProperty(propName)
    ) {
      props[propName] = config[propName];
    }
  }

  // 处理默认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
  )
}

const ReactElement = function(type, key, ref, self, source, owner, props) {
  const element = {
    // 表示是否为ReactElement
    $$typeof: REACT_ELEMENT_TYPE,

    // 元素自身属性
    type: type,
    key: key,
    ref: ref,
    props: props,

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

  if (__DEV__) {
    element._store = {};

    // 开发环境下将_store、_self、_source属性变为不可枚举
    Object.defineProperty(element._store, 'validated', {
      configurable: false,
      enumerable: false,
      writable: true,
      value: false,
    });

    Object.defineProperty(element, '_self', {
      configurable: false,
      enumerable: false,
      writable: false,
      value: self,
    });

    Object.defineProperty(element, '_source', {
      configurable: false,
      enumerable: false,
      writable: false,
      value: source,
    });
    // 冻结props、element防止被手动修改
    if (Object.freeze) {
      Object.freeze(element.props);
      Object.freeze(element);
    }
  }

  return element;
};

// packages/react/src/ReactElement.js
export function createElement(type, config, children) {
  let propName;

  // 记录标签上的属性集合
  const props = {};

  //单独处理key ref
  let key = null;
  let ref = null;
  let self = null;
  let source = null;

  // 当config部位null的时候，表示标签上有属性，加到props里面去
  if (config != null) {
    // 合法的ref才做处理
    if (hasValidRef(config)) {
      ref = config.ref;

      if (__DEV__) {
        warnIfStringRefCannotBeAutoConverted(config);
      }
    }
    if (hasValidKey(config)) {
      // 有合法的key才做处理
      key = '' + config.key;
    }

    // 记录信息用于debug
    self = config.__self === undefined ? null : config.__self;
    source = config.__source === undefined ? null : config.__source;

    // 处理self，source，key，ref以外的属性，加入props中
    for (propName in config) {
      if (
        hasOwnProperty.call(config, propName) &&
        !RESERVED_PROPS.hasOwnProperty(propName)
      ) {
        props[propName] = config[propName];
      }
    }
  }

  // 处理子节点
  const childrenLength = arguments.length - 2;
  // 单标签子节点
  if (childrenLength === 1) {
    props.children = children;
    //嵌套子节点
  } else if (childrenLength > 1) {
    const childArray = Array(childrenLength);
    for (let i = 0; i < childrenLength; i++) {
      childArray[i] = arguments[i + 2];
    }
    //开发环境冻结，childArray防止被修改
    if (__DEV__) {
      if (Object.freeze) {
        Object.freeze(childArray);
      }
    }
    props.children = childArray;
  }

  // 处理默认props
  if (type && type.defaultProps) {
    const defaultProps = type.defaultProps;
    for (propName in defaultProps) {
      if (props[propName] === undefined) {
        props[propName] = defaultProps[propName];
      }
    }
  }
  if (__DEV__) {
    // dev环境下，key 与 ref不挂到props中去
    if (key || ref) {
      const displayName =
        typeof type === 'function'
          ? type.displayName || type.name || 'Unknown'
          : type;
      if (key) {
        defineKeyPropWarningGetter(props, displayName);
      }
      if (ref) {
        defineRefPropWarningGetter(props, displayName);
      }
    }
  }
  // 调用返回
  return ReactElement(
    type,
    key,
    ref,
    self,
    source,
    ReactCurrentOwner.current,
    props,
  );
}

const ReactElement = function(type, key, ref, self, source, owner, props) {
  const element = {
    // This tag allows us to uniquely identify this as a React Element
    $$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,
  };

  if (__DEV__) {
    // The validation flag is currently mutative. We put it on
    // an external backing store so that we can freeze the whole object.
    // This can be replaced with a WeakMap once they are implemented in
    // commonly used development environments.
    element._store = {};

    // To make comparing ReactElements easier for testing purposes, we make
    // the validation flag non-enumerable (where possible, which should
    // include every environment we run tests in), so the test framework
    // ignores it.
    Object.defineProperty(element._store, 'validated', {
      configurable: false,
      enumerable: false,
      writable: true,
      value: false,
    });
    // self and source are DEV only properties.
    Object.defineProperty(element, '_self', {
      configurable: false,
      enumerable: false,
      writable: false,
      value: self,
    });
    // Two elements created in two different places should be considered
    // equal for testing purposes and therefore we hide it from enumeration.
    Object.defineProperty(element, '_source', {
      configurable: false,
      enumerable: false,
      writable: false,
      value: source,
    });
    if (Object.freeze) {
      Object.freeze(element.props);
      Object.freeze(element);
    }
  }

  return element;
};

// packages/react/src/ReactBaseClasses.js
function Component(props, context, updater) {
  // 接受各种参数,挂到this上
  this.props = props;
  this.context = context;
  this.refs = emptyObject;
  // updater ?? 
  this.updater = updater || ReactNoopUpdateQueue;
}

// 原型上挂载了isReactComponent用来区分函数组件与类组件
Component.prototype.isReactComponent = {};

//原型上挂载了setState方法用来触发更新
Component.prototype.setState = function(partialState, callback) {
  invariant(
    typeof partialState === 'object' ||
      typeof partialState === 'function' ||
      partialState == null,
    'setState(...): takes an object of state variables to update or a ' +
      'function which returns an object of state variables.',
  );
  // 调用updater上的enqueueSetState方法？？？
  this.updater.enqueueSetState(this, partialState, callback, 'setState');
};

// 原型上挂载了强制更新的方法
Component.prototype.forceUpdate = function(callback) {
  this.updater.enqueueForceUpdate(this, callback, 'forceUpdate');
};