class App extends Component {
render() {
return (
<div className="App">
<header className="App-header">
<img src={logo} className="App-logo" alt="logo" />
<p>
Edit <code>src/App.js</code> and save to reload.
</p>
<a
className="App-link"
href="https://reactjs.org"
target="_blank"
rel="noopener noreferrer"
>
Learn React
</a>
</header>
</div>
);
}
}
function Welcome(props) {
return <h1>Hello, {props.name}</h1>;
}
class Welcome extends React.Component {
render() {
return <h1>Hello, {this.props.name}</h1>;
}
}
render进行return时,对于单行的内容,没必要加括号,但对于多行的内容要加括号
原因在于,JSX转为js后,js会在每行自动加';'
,如果return后换行了,那么就会变成return;
下面通过babel来做一下编译:
class Welcome extends React.Component {
render() {
return <h1>Hello, {this.props.name}</h1>;
}
}
//********************
var Welcome = /*#__PURE__*/function (_React$Component) {
_inherits(Welcome, _React$Component);
var _super = _createSuper(Welcome);
function Welcome() {
_classCallCheck(this, Welcome);
return _super.apply(this, arguments);
}
_createClass(Welcome, [{
key: "render",
value: function render() {
return /*#__PURE__*/React.createElement("h1", null, "Hello, ", this.props.name);
}
}]);
return Welcome;
}(React.Component);
做下对比
class Welcome extends React.Component {
render() {
return
<h1>Hello, {this.props.name}</h1>;
}
}
//******************
var Welcome = /*#__PURE__*/function (_React$Component) {
_inherits(Welcome, _React$Component);
var _super = _createSuper(Welcome);
function Welcome() {
_classCallCheck(this, Welcome);
return _super.apply(this, arguments);
}
_createClass(Welcome, [{
key: "render",
value: function render() {
return;
/*#__PURE__*/
React.createElement("h1", null, "Hello, ", this.props.name);
}
}]);
return Welcome;
}(React.Component);
所以针对文章开头举的app的例子,如果不加括号的话,是需要右内容和return在同一行的,就像下面这样
class App extends Component {
render() {
return <div className="App">
<header className="App-header">
<img src={logo} className="App-logo" alt="logo" />
<p>
Edit <code>src/App.js</code> and save to reload.
</p>
<a
className="App-link"
href="https://reactjs.org"
target="_blank"
rel="noopener noreferrer"
>
Learn React
</a>
</header>
</div>
}
}
这样写也是可以编译通过的,但如果不加括号,还在return后换行了,那就会报错
class App extends Component {
render() {
return
<div className="App">
<header className="App-header">
<img src={logo} className="App-logo" alt="logo" />
<p>
Edit <code>src/App.js</code> and save to reload.
</p>
<a
className="App-link"
href="https://reactjs.org"
target="_blank"
rel="noopener noreferrer"
>
Learn React
</a>
</header>
</div>
}
}
另外还要注意的一点是,对于return的内容,只能有一个根节点,所以返回的内容必须有一个tag进行包裹,否则,不管加不加括号都是不行的,编译报错的描述也很直观了