function Mailbox(props) {
const unreadMessages = props.unreadMessages; //這裏是我容易搞混的地方,props.屬性名
return (
<div>
<h1>Hello!</h1>
{unreadMessages.length > 0 &&
<h2>
You have {unreadMessages.length} unread messages.
</h2>
}
</div>
);
}
const messages = ['React', 'Re: React', 'Re:Re: React'];
ReactDOM.render(
<Mailbox unreadMessages={messages} />, //這裏的屬性再被傳入子組件時被稱爲props.unreadMessages
document.getElementById('root')
);
class LoginControl extends React.Component {
constructor(props) {
super(props);
this.handleLoginClick = this.handleLoginClick.bind(this);
this.handleLogoutClick = this.handleLogoutClick.bind(this);
this.state = {isLoggedIn: false};
}
handleLoginClick() {
this.setState({isLoggedIn: true});
}
handleLogoutClick() {
this.setState({isLoggedIn: false});
}
render() {
const isLoggedIn = this.state.isLoggedIn;
let button = null;
if (isLoggedIn) {
button = <LogoutButton onClick={this.handleLogoutClick} />;
} else {
button = <LoginButton onClick={this.handleLoginClick} />;
}
return (
<div>
<Greeting isLoggedIn={isLoggedIn} />
{button}
</div>
);
}
}
function UserGreeting(props) {
return <h1>Welcome back!</h1>;
}
function GuestGreeting(props) {
return <h1>Please sign up.</h1>;
}
function Greeting(props) {
const isLoggedIn = props.isLoggedIn;
if (isLoggedIn) {
return <UserGreeting />;
}
return <GuestGreeting />;
}
function LoginButton(props) {
return (
<button onClick={props.onClick}>
Login
</button>
);
}
function LogoutButton(props) {
return (
<button onClick={props.onClick}>
Logout
</button>
);
}
ReactDOM.render(
<LoginControl />,
document.getElementById('root')
);
function WarningBanner(props) {
if (!props.warn) { {/*當warn爲false時返回空*/}
return null;
}
return (
<div className="warning">
Warning!
</div>
);
}
class Page extends React.Component {
constructor(props) {
super(props);
this.state = {showWarning: true}
this.handleToggleClick = this.handleToggleClick.bind(this);
}
handleToggleClick() {
this.setState(prevState => ({
showWarning: !prevState.showWarning
}));
}
render() {
return (
<div>
<WarningBanner warn={this.state.showWarning} /> {/*屬性warn*/}
<button onClick={this.handleToggleClick}>
{this.state.showWarning ? 'Hide' : 'Show'}
</button>
</div>
);
}
}
ReactDOM.render(
<Page />,
document.getElementById('root')
);