深い学習を反応させ:. 2コンポーネント、PureComponent

見てみましょうの公式サイトリアクト最初のサンプルコードを：

class ShoppingList extends React.Component {
  render() {
    return (
      <div className="shopping-list">
        <h1>Shopping List for {this.props.name}</h1>
        <ul>
          <li>Instagram</li>
          <li>WhatsApp</li>
          <li>Oculus</li>
        </ul>
      </div>
    );
  }
}

// 用法示例: <ShoppingList name="Mark" />
复制代码

で作成された反応アセンブリ、次の方法：

機能の
クラスの方法
React.createElement

上記のコードでコンポーネントアプローチを作成するために使用されるクラスに属します。のは、React.Componentソースを見てみましょう。

ソース

ソースの場所：パッケージ/反応/ SRC / ReactBaseClasses.js

/**
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */

import invariant from 'shared/invariant';
import lowPriorityWarning from 'shared/lowPriorityWarning';

import ReactNoopUpdateQueue from './ReactNoopUpdateQueue';

const emptyObject = {};
if (__DEV__) {
  Object.freeze(emptyObject);
}

/**
 * Base class helpers for the updating state of a component.
 */
function Component(props, context, updater) {
  this.props = props;
  this.context = context;
  // If a component has string refs, we will assign a different object later.
  this.refs = emptyObject;
  // We initialize the default updater but the real one gets injected by the
  // renderer.
  this.updater = updater || ReactNoopUpdateQueue;
}

Component.prototype.isReactComponent = {};

/**
 * Sets a subset of the state. Always use this to mutate
 * state. You should treat `this.state` as immutable.
 *
 * There is no guarantee that `this.state` will be immediately updated, so
 * accessing `this.state` after calling this method may return the old value.
 *
 * There is no guarantee that calls to `setState` will run synchronously,
 * as they may eventually be batched together.  You can provide an optional
 * callback that will be executed when the call to setState is actually
 * completed.
 *
 * When a function is provided to setState, it will be called at some point in
 * the future (not synchronously). It will be called with the up to date
 * component arguments (state, props, context). These values can be different
 * from this.* because your function may be called after receiveProps but before
 * shouldComponentUpdate, and this new state, props, and context will not yet be
 * assigned to this.
 *
 * @param {object|function} partialState Next partial state or function to
 *        produce next partial state to be merged with current state.
 * @param {?function} callback Called after state is updated.
 * @final
 * @protected
 */
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.',
  );
  this.updater.enqueueSetState(this, partialState, callback, 'setState');
};

/**
 * Forces an update. This should only be invoked when it is known with
 * certainty that we are **not** in a DOM transaction.
 *
 * You may want to call this when you know that some deeper aspect of the
 * component's state has changed but `setState` was not called.
 *
 * This will not invoke `shouldComponentUpdate`, but it will invoke
 * `componentWillUpdate` and `componentDidUpdate`.
 *
 * @param {?function} callback Called after update is complete.
 * @final
 * @protected
 */
Component.prototype.forceUpdate = function(callback) {
  this.updater.enqueueForceUpdate(this, callback, 'forceUpdate');
};

/**
 * Deprecated APIs. These APIs used to exist on classic React classes but since
 * we would like to deprecate them, we're not going to move them over to this
 * modern base class. Instead, we define a getter that warns if it's accessed.
 */
if (__DEV__) {
  const deprecatedAPIs = {
    isMounted: [
      'isMounted',
      'Instead, make sure to clean up subscriptions and pending requests in ' +
        'componentWillUnmount to prevent memory leaks.',
    ],
    replaceState: [
      'replaceState',
      'Refactor your code to use setState instead (see ' +
        'https://github.com/facebook/react/issues/3236).',
    ],
  };
  const defineDeprecationWarning = function(methodName, info) {
    Object.defineProperty(Component.prototype, methodName, {
      get: function() {
        lowPriorityWarning(
          false,
          '%s(...) is deprecated in plain JavaScript React classes. %s',
          info[0],
          info[1],
        );
        return undefined;
      },
    });
  };
  for (const fnName in deprecatedAPIs) {
    if (deprecatedAPIs.hasOwnProperty(fnName)) {
      defineDeprecationWarning(fnName, deprecatedAPIs[fnName]);
    }
  }
}

function ComponentDummy() {}
ComponentDummy.prototype = Component.prototype;

/**
 * Convenience component with default shallow equality check for sCU.
 */
function PureComponent(props, context, updater) {
  this.props = props;
  this.context = context;
  // If a component has string refs, we will assign a different object later.
  this.refs = emptyObject;
  this.updater = updater || ReactNoopUpdateQueue;
}

const pureComponentPrototype = (PureComponent.prototype = new ComponentDummy());
pureComponentPrototype.constructor = PureComponent;
// Avoid an extra prototype jump for these methods.
Object.assign(pureComponentPrototype, Component.prototype);
pureComponentPrototype.isPureReactComponent = true;

export {Component, PureComponent};
复制代码

これは、ソースコード含まComponentとPureComponentソースコード。

成分

それが自然に上の図のプロトタイピングを持つ属性のすべてのインスタンスをインスタンス化されShoppingListアセンブリ。

コンポーネントを使用します。

<ShoppingList name="Mark" />复制代码

このコードを参照してください、いくつかの質問を生成します。

継承Componentコンポーネントがどのように行う、その後、インスタンス化されますか？
ES6他のクラスから継承し、明示的にクラスのインスタンス化のニーズを呼び出すsuper()あなたはそれで反応する必要はありませんなぜ、？

JSX

JSX構文で構文上で定義しShoppingListコンポーネント。では-depth JSXを述べた章、JSXだけReact.createElement(component, props, ...children)糖衣構文機能。それは最終的にコンパイルされます機能。React.createElement

<MyButton color="blue" shadowSize={2}>
  Click Me
</MyButton>复制代码

これは次のようにコンパイルされます。

React.createElement(
  MyButton,
  {color: 'blue', shadowSize: 2},
  'Click Me'
)复制代码

JSXこと、それはどのようにコンパイルされていますか？

プロジェクト内のJSXは似ています @babel/plugin-transform-react-jsx し、後で章を勉強し、このプラグインについてのコンパイルバベルのプラグイン。

最後に、すべてが指す React.createElement機能、次の章では、我々は見ていきます React.createElement

PurComponent

基本的にはとComponent同じ

ます。https：//juejin.im/post/5cef33076fb9a07eb74b1ff9で再現

深い学習を反応させ:. 2コンポーネント、PureComponent

ソース

成分

JSX

PurComponent

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