我的阅读目录
2-3 create-element
路径
react/packages/react/src/ReactElement.js
核心数据结构
ReactElement
1. 定义了一个对象 element
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,
};
- DEV 模式中还有其他操作
- 其他属性:
// 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,
});
注:涉及知识点 ES6 Object.defineProperty developer.mozilla.org/zh-CN/docs/…
- freeze 冻结 props 和 element.
if (Object.freeze) {
Object.freeze(element.props);
Object.freeze(element);
}
核心 API
1. JSX 语法到 React.createElement
工具准备:babeljs.io/
2. create-element
create-element 将我们写的(jsx 转换后的),转换为 ReactElement 数据结构。
- 入参 type, config, children.
- 出参 ReactElement()
代码执行部分:
2.1 数据初始化
2.2 数据校验
- hasValidRef
- hasValidKey
2.3 数据转换
- 原型上的其他属性
for (propName in config) {
if (
hasOwnProperty.call(config, propName) &&
!RESERVED_PROPS.hasOwnProperty(propName)
) {
props[propName] = config[propName];
}
}
- 对 children 处理.
- defaultProps 填充到空的 props 里。
2.4 数据传入 ReactElement 生成实例
附录:源码
react/packages/react/src/ReactElement.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 getComponentName from 'shared/getComponentName';
import invariant from 'shared/invariant';
import {REACT_ELEMENT_TYPE} from 'shared/ReactSymbols';
import ReactCurrentOwner from './ReactCurrentOwner';
const hasOwnProperty = Object.prototype.hasOwnProperty;
const RESERVED_PROPS = {
key: true,
ref: true,
__self: true,
__source: true,
};
let specialPropKeyWarningShown,
specialPropRefWarningShown,
didWarnAboutStringRefs;
if (__DEV__) {
didWarnAboutStringRefs = {};
}
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;
}
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;
}
function defineKeyPropWarningGetter(props, displayName) {
const warnAboutAccessingKey = function() {
if (__DEV__) {
if (!specialPropKeyWarningShown) {
specialPropKeyWarningShown = true;
console.error(
'%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://reactjs.org/link/special-props)',
displayName,
);
}
}
};
warnAboutAccessingKey.isReactWarning = true;
Object.defineProperty(props, 'key', {
get: warnAboutAccessingKey,
configurable: true,
});
}
function defineRefPropWarningGetter(props, displayName) {
const warnAboutAccessingRef = function() {
if (__DEV__) {
if (!specialPropRefWarningShown) {
specialPropRefWarningShown = true;
console.error(
'%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://reactjs.org/link/special-props)',
displayName,
);
}
}
};
warnAboutAccessingRef.isReactWarning = true;
Object.defineProperty(props, 'ref', {
get: warnAboutAccessingRef,
configurable: true,
});
}
function warnIfStringRefCannotBeAutoConverted(config) {
if (__DEV__) {
if (
typeof config.ref === 'string' &&
ReactCurrentOwner.current &&
config.__self &&
ReactCurrentOwner.current.stateNode !== config.__self
) {
const componentName = getComponentName(ReactCurrentOwner.current.type);
if (!didWarnAboutStringRefs[componentName]) {
console.error(
'Component "%s" contains the string ref "%s". ' +
'Support for string refs will be removed in a future major release. ' +
'This case cannot be automatically converted to an arrow function. ' +
'We ask you to manually fix this case by using useRef() or createRef() instead. ' +
'Learn more about using refs safely here: ' +
'https://reactjs.org/link/strict-mode-string-ref',
componentName,
config.ref,
);
didWarnAboutStringRefs[componentName] = true;
}
}
}
}
/**
* Factory method to create a new React element. This no longer adheres to
* the class pattern, so do not use new to call it. Also, instanceof check
* will not work. Instead test $typeof field against Symbol.for('react.element') to check
* if something is a React Element.
*
* @param {*} type
* @param {*} props
* @param {*} key
* @param {string|object} ref
* @param {*} owner
* @param {*} self A *temporary* helper to detect places where `this` is
* different from the `owner` when React.createElement is called, so that we
* can warn. We want to get rid of owner and replace string `ref`s with arrow
* functions, and as long as `this` and owner are the same, there will be no
* change in behavior.
* @param {*} source An annotation object (added by a transpiler or otherwise)
* indicating filename, line number, and/or other information.
* @internal
*/
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;
};
/**
* https://github.com/reactjs/rfcs/pull/107
* @param {*} type
* @param {object} props
* @param {string} key
*/
export function jsx(type, config, maybeKey) {
let propName;
// Reserved names are extracted
const props = {};
let key = null;
let ref = null;
// Currently, key can be spread in as a prop. This causes a potential
// issue if key is also explicitly declared (ie. <div {...props} key="Hi" />
// or <div key="Hi" {...props} /> ). We want to deprecate key spread,
// but as an intermediary step, we will use jsxDEV for everything except
// <div {...props} key="Hi" />, because we aren't currently able to tell if
// key is explicitly declared to be undefined or not.
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,
);
}
/**
* https://github.com/reactjs/rfcs/pull/107
* @param {*} type
* @param {object} props
* @param {string} key
*/
export function jsxDEV(type, config, maybeKey, source, self) {
let propName;
// Reserved names are extracted
const props = {};
let key = null;
let ref = null;
// Currently, key can be spread in as a prop. This causes a potential
// issue if key is also explicitly declared (ie. <div {...props} key="Hi" />
// or <div key="Hi" {...props} /> ). We want to deprecate key spread,
// but as an intermediary step, we will use jsxDEV for everything except
// <div {...props} key="Hi" />, because we aren't currently able to tell if
// key is explicitly declared to be undefined or not.
if (maybeKey !== undefined) {
key = '' + maybeKey;
}
if (hasValidKey(config)) {
key = '' + config.key;
}
if (hasValidRef(config)) {
ref = config.ref;
warnIfStringRefCannotBeAutoConverted(config);
}
// 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];
}
}
}
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,
);
}
/**
* 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;
// 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 (__DEV__) {
warnIfStringRefCannotBeAutoConverted(config);
}
}
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,
);
}
/**
* Return a function that produces ReactElements of a given type.
* See https://reactjs.org/docs/react-api.html#createfactory
*/
export function createFactory(type) {
const factory = createElement.bind(null, type);
// Expose the type on the factory and the prototype so that it can be
// easily accessed on elements. E.g. `<Foo />.type === Foo`.
// This should not be named `constructor` since this may not be the function
// that created the element, and it may not even be a constructor.
// Legacy hook: remove it
factory.type = type;
return factory;
}
export function cloneAndReplaceKey(oldElement, newKey) {
const newElement = ReactElement(
oldElement.type,
newKey,
oldElement.ref,
oldElement._self,
oldElement._source,
oldElement._owner,
oldElement.props,
);
return newElement;
}
/**
* Clone and return a new ReactElement using element as the starting point.
* See https://reactjs.org/docs/react-api.html#cloneelement
*/
export function cloneElement(element, config, children) {
invariant(
!(element === null || element === undefined),
'React.cloneElement(...): The argument must be a React element, but you passed %s.',
element,
);
let propName;
// Original props are copied
const props = Object.assign({}, element.props);
// Reserved names are extracted
let key = element.key;
let ref = element.ref;
// Self is preserved since the owner is preserved.
const self = element._self;
// Source is preserved since cloneElement is unlikely to be targeted by a
// transpiler, and the original source is probably a better indicator of the
// true owner.
const source = element._source;
// Owner will be preserved, unless ref is overridden
let owner = element._owner;
if (config != null) {
if (hasValidRef(config)) {
// Silently steal the ref from the parent.
ref = config.ref;
owner = ReactCurrentOwner.current;
}
if (hasValidKey(config)) {
key = '' + config.key;
}
// Remaining properties override existing props
let defaultProps;
if (element.type && element.type.defaultProps) {
defaultProps = element.type.defaultProps;
}
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];
}
}
}
}
// 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];
}
props.children = childArray;
}
return ReactElement(element.type, key, ref, self, source, owner, props);
}
/**
* Verifies the object is a ReactElement.
* See https://reactjs.org/docs/react-api.html#isvalidelement
* @param {?object} object
* @return {boolean} True if `object` is a ReactElement.
* @final
*/
export function isValidElement(object) {
return (
typeof object === 'object' &&
object !== null &&
object.$typeof === REACT_ELEMENT_TYPE
);
}
注:作者第一次开始写 blog,文笔等问题望见谅。暂时作为自学、写东西的地儿。