其实呢,jsx语法中,react并不是用new的形式来创建组件,而是使用React.createElement来创建组件的,所以当你在使用
<Person />
这种语法来书写组件时,其实解析出来的形式为:
React.createElement(Person,null,null)
而我们写:
<div>这里是文字</div>
最终编译解析成:
React.createElement('div',null,'这里是文字')
而如果你需要往person里面添加一些props的属性,jsx的语法为:
<Person
name='Jack'
/>
而解析出来的语法为:
React.createElement(Person,{name : 'jack'},null)
而当我们div之间有多个嵌套的最终解析会如何,例如下面的写法:
<div>
<h2>这里是标题</h2>
<p>这里是内容</p>
</div>
而jsx最终解析为:
React.createElement('div',null,React.createElement('h2',null,'这里是标题'),React.createElement('p',null,'这里是内容'))
React文档中提到,React.createElement方法提供三个参数:
React.createElement(
type,
[props],
[...children]
)
第一个参数为组件的类型,小写则为原生的提供的组件,大写则为自定义的组件
第二个参数为传入的props
第三个参数则为children,传入的为子元素的解析
而这三个参数可以完美适应所有的jsx的书写方式,另附react官方文档:
React Without JSX
附录2:React.createElement方法的源码,
//createElement 方法的源码
ReactElement.createElement = function (type, config, children) {
var propName;
// Reserved names are extracted
var props = {};
var key = null;
var ref = null;
var self = null;
var 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.
var childrenLength = arguments.length - 2;
if (childrenLength === 1) {
props.children = children;
} else if (childrenLength > 1) {
var childArray = Array(childrenLength);
for (var i = 0; i < childrenLength; i++) {
childArray[i] = arguments[i + 2];
}
if (process.env.NODE_ENV !== 'production') {
if (Object.freeze) {
Object.freeze(childArray);
}
}
props.children = childArray;
}
// Resolve default props
if (type && type.defaultProps) {
var defaultProps = type.defaultProps;
for (propName in defaultProps) {
if (props[propName] === undefined) {
props[propName] = defaultProps[propName];
}
}
}
if (process.env.NODE_ENV !== 'production') {
if (key || ref) {
if (typeof props.$$typeof === 'undefined' || props.$$typeof !== REACT_ELEMENT_TYPE) {
var 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);
};
//最终返回的ReactElement,顺便附带注释吧
/**
* 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, no instanceof check
* will work. Instead test $$typeof field against Symbol.for('react.element') to check
* if something is a React Element.
*
* @param {*} type
* @param {*} key
* @param {string|object} ref
* @param {*} self A *temporary* helper to detect places where `this` is
* different from the `owner` when React.createElement is called, so that we
* can warn. We want to get rid of owner and replace string `ref`s with arrow
* functions, and as long as `this` and owner are the same, there will be no
* change in behavior.
* @param {*} source An annotation object (added by a transpiler or otherwise)
* indicating filename, line number, and/or other information.
* @param {*} owner
* @param {*} props
* @internal
*/
var ReactElement = function (type, key, ref, self, source, owner, props) {
var element = {
// This tag allow us to uniquely identify this as a React Element
$$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 (process.env.NODE_ENV !== 'production') {
// 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.
if (canDefineProperty) {
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
});
} else {
element._store.validated = false;
element._self = self;
element._source = source;
}
if (Object.freeze) {
Object.freeze(element.props);
Object.freeze(element);
}
}
return element;
};
看看这个其实就可以理解了