问题
Recently, I've started tinkering with React.js and I love it. I started out in the regular ES5, so as to get the hang of things, the docs are all written in ES5...
But now I wanted to try ES6, because it's shiny and new, and it does seem to simplify some things. What bothers me a lot is that for every method I had added into my component classes I now have to bind 'this' to, otherwise it doesn't work. So my constructor ends up looking like this:
constructor(props) {
super(props);
this.state = { ...some initial state... }
this.someHandler = this.someHandler.bind(this);
this.someHandler = this.someHandler.bind(this);
this.someHandler = this.someHandler.bind(this);
this.someHandler = this.someHandler.bind(this);
this.someHandler = this.someHandler.bind(this);
this.someHandler = this.someHandler.bind(this);
this.someHandler = this.someHandler.bind(this);
}
If I were to add even more methods to my class, this would become an even bigger, uglier mess.
My question is, is there some way to get around this, or at least make it easier, shorter and less ugly? One of the main reasons I wanted to try React with ES6 was to make my code more concise, but this is doing the opposite. Any suggestions or input would be appreciated.
回答1:
You can use class fields to do the binding outside the constructor. They look like the following:
class Foo extends React.Component {
handleBar = () => {
console.log('neat');
};
handleFoo = () => {
console.log('cool');
};
render() {
return (
<div
onClick={this.handleBar}
onMouseOver={this.handleFoo}
/>
);
}
}
Class fields are supported experimentally by Babel via its class properties transform, but they are still "experimental" because they are a Stage 3 Draft (not yet in a Babel preset).
You will need to do the binding manually until ES7 or until enabling the feature in Babel, however. This topic is covered briefly in Babel's blog post on React on ES6+.
回答2:
Another alternative is to use decorators. You declare a getter on the prototype, and on first access for an instance it defines an own property with a bound version of that function.
But there's a catch! In development it won't replace the property, it'll bind on every access. This means you don't break react-hot-loader. At least for me, that's pretty important.
I created a library, class-bind, that provides this.
import {bound} from 'class-bind';
class App {
constructor(){
this.foo = 'bar';
}
@bound
returnsFoo(){
return this.foo;
}
render(){
var returnsFoo = this.returnsFoo;
return (
<div>
{returnsFoo()} === 'bar'
</div>
);
}
}
Decorators too unstable for you? You can bind everything or some things with the same benefits.
import {bind, bindAll} from 'class-bind';
bind(App.prototype, 'returnsFoo');
// or
bindAll(App.prototype);
回答3:
Ssorallen's suggestion is great but if you want another way there is:
class AppCtrlRender extends Component {
binder(...methods) { methods.forEach( (method) => this[method] = this[method].bind(this) ); }
render() {
var isMobile = this.state.appData.isMobile;
var messages = this.state.appData.messages;
return (
<div id='AppCtrlSty' style={AppCtrlSty}>
React 1.3 Slider
<br/><br/>
<div className='FlexBoxWrap'>
<Slider isMobile={isMobile}/>
<JList data={messages}/>
</div>
</div>
);
}
}
var getAppState = function() {
return {
appData: AppStore.getAppData()
};
};
export default class AppCtrl extends AppCtrlRender {
constructor() {
super();
this.state = getAppState();
this.binder('appStoreDidChange');
}
componentDidMount() {
var navPlatform = window.navigator.platform;
Actions.setWindowDefaults(navPlatform);
}
componentWillMount() { AppStore.onAny(this.appStoreDidChange); }
componentWillUnmount() { AppStore.offAny(this.appStoreDidChange); }
appStoreDidChange() { this.setState(getAppState()); }
}
You can add any number of methods to this.binder('method1', 'method2', ...)
回答4:
If you use stage-0 there is a function binding syntax.
class MyComp extends Component {
handleClick() { console.log('doing things') }
render() {
return <button onClick={::this.handleClick}>Do Things</button>
}
}
This destructures to this.handleClick.call(this), which I think is generally performant enough.
回答5:
One idea to avoid bind
class MyComp extends Component {
render() {
return <button onClick={e => this.handleClick(e)}>Do Things</button>
}
}
disclaimer: untested, also, cannot easily handle more than one argument (in this case, there is one, event (e).
Also, this is answer is probably an example of what not to do, according to this article which is probably a worthwhile read:
https://daveceddia.com/avoid-bind-when-passing-props/
回答6:
I actually prefer to imitate OOP inheritance by passing children the parent context.
class Parent extends Component {
state = {happy: false}
changeState(happy) {
this.setState({happy})
}
render() {
return (
<Child parent={this} >
)
}
}
class Child extends Component {
//...
this.props.parent.changeState(true)
}
$0.02, Jon
回答7:
I created a method to organize all the "binds".
class MyClass {
constructor() {
this.bindMethods([
'updateLocationFields',
'render',
'loadCities',
]);
}
bindMethods(methods) {
methods.forEach((item) => {
this[item] = this[item].bind(this);
});
}
...
}
回答8:
I use a helper function doBinding(this), which I call in each constructor. In this example it binds _handleChange1() and _handleChange2().
class NameForm extends React.Component {
constructor(props) {
super(props);
doBinding(this);
this.state = {value1: "", value2: ""};
}
_handleChange1(event) {
this.setState({value1: event.target.value});
}
_handleChange2(event) {
this.setState({value2: event.target.value});
}
render() {
...
}
}
The method works even if you are not using Babel.
My handler methods all begin with _ (a convention to indicate they are private). So doBinding() looks for the _. You can remove the if (key.startsWith("_")) if you don't use this convention.
function doBinding(obj) {
const proto = Object.getPrototypeOf(obj);
for (const key of Object.getOwnPropertyNames(proto)) {
if (key.startsWith("_")) {
obj[key] = obj[key].bind(obj);
}
}
}
来源：https://stackoverflow.com/questions/32192682/react-js-es6-avoid-binding-this-to-every-method