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React源码阅读-13_044

更新时间:2019-11-12

React 源码阅读-13

React Element

ReactElement.png

Function

Object.getOwnPropertyDescriptor() 方法返回指定对象上一个自有属性对应的属性描述符

Object.defineProperty() 方法会直接在一个对象上定义一个新属性,或者修改一个对象的现有属性, 并返回这个对象。

hasValidRef

判断是否有有效的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

判断是否有有效的 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 = {
    // 这个标签使我们可以唯一地将其标识为React Element
    $$typeof: REACT_ELEMENT_TYPE,

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

    // 记录负责创建此元素的组件。
    _owner: owner,
  };

  if (__DEV__) {
    //验证标志当前是可变的。我们穿上
    //外部后备存储,以便我们可以冻结整个对象。
    //可以在WeakMap中实现后,将其替换为WeakMap
    //常用的开发环境。
    element._store = {};

    //为了便于比较ReactElement以进行测试,我们使
    //验证标志不可枚举(在可能的情况下,应
    //包括我们在其中运行测试的所有环境),因此测试框架
    //忽略它。
    Object.defineProperty(element._store, 'validated', {
      configurable: false,
      enumerable: false,
      writable: true,
      value: false,
    });
    // self和source是仅DEV的属性。
    Object.defineProperty(element, '_self', {
      configurable: false,
      enumerable: false,
      writable: false,
      value: self,
    });

    //应该考虑在两个不同位置创建的两个元素
    //出于测试目的是相等的,因此我们将其从枚举中隐藏起来。
    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;

  //当前,key可以作为props传播。这导致潜在的
  //如果还明确声明了key,则会出现问题(即<div {... props} key =“ Hi” />
  //或<div key =“ Hi” {... props} />)。我们要弃用key传值,
  //但作为中介步骤,我们将对所有内容使用jsxDEV
  //<div {... props} key =“ Hi” />,因为我们目前无法确定是否
  //key已明确声明为未定义。

  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defineKeyPropWarningGetterdefineRefPropWarningGetter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

此辅助函数已废弃

export function createFactory(type) {
  const factory = createElement.bind(null, type);
  //公开工厂和原型上的类型,以便可以
  //易于访问的元素。例如。 `<Foo />.type === Foo`。
  //不应将其命名为“ constructor”,因为它可能不是函数
  //创建了元素,甚至可能不是构造函数。
  //旧版挂钩:将其删除
  factory.type = type;
  return factory;
}

cloneElement

element 元素为样板克隆并返回新的 React 元素。返回元素的 props 是将新的 props 与原始元素的 props 浅层合并后的结果。新的子元素将取代现有的子元素,而来自原始元素的 keyref 将被保留。

isValidElement

验证对象是否为 React 元素,返回值为 truefalse

export function isValidElement(object) {
  // typeof null = object
  return (
    typeof object === 'object' &&
    object !== null &&
    object.$$typeof === REACT_ELEMENT_TYPE
  );
}
https://zh-hans.reactjs.org/d...

原文链接:https://segmentfault.com/a/1190000020971927

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