有没有办法在外部传递函数内部的变量 [英] is there a way to pass variable inside of a function outside in react
问题描述
我是新来的反应者,我正在尝试制作一个简单的倒计时应用程序.但是在反应中,我不知道如何为所有可以对其求值的函数提供一个全局变量.请看一下我的代码,无论如何,我可以使暂停和继续按钮起作用吗?在普通的javascript中,我可以将timer设置为全局变量,并从另一个函数访问它,这样,我可以在需要时在timer上调用clearInterval,但是在响应中,我不知道如何调用clearInterval来使Timer暂停开始功能,因为它被限制在开始功能块中.
I am new to react, and I am trying to make a simple countdown app. but in react, I don't know how to give a global variable for all the functions can get assess to it. Please take a look at my code, is there anyway I can make the pause and the continue buttons work? In plain javascript I can set timer as a global variable and get access to it from another function, by that, I can call clearInterval on timer when I want, but in react I don't know how to call clearInterval for timer to pause begin function since it is restricted in the begin function block.
import React from 'react';
import ReactDOM from 'react-dom';
class Countdown extends React.Component{
render(){
return(
<div>
<button onClick={()=>begin()}>start</button>
<button>pause</button>
<button>continue</button>
</div>
);
}
};
const begin=(props)=>{
let count = 10;
const timer = setInterval(countdown,1000);
function countdown(){
count=count-1
if (count<0){
clearInterval(timer);
return;
}
console.log(count)
}
}
ReactDOM.render(<Countdown/>, document.getElementById('app'));
推荐答案
您可以这样做:
class Countdown extends React.Component{
constructor() {
super();
//set the initial state
this.state = { count: 10 };
}
//function to change the state
changeCount(num){
this.setState({count:num});
}
render(){
return(
<div>
<button onClick={()=>begin(this.changeCount.bind(this), this.state.count)}>start</button>
<button>pause</button>
<button>continue</button>
<p>{this.state.count}</p>
</div>
);
}
};
//callback function to change the state in component
//c is the initial count in state
const begin=(fun, c)=>{
let count = c;
const timer = setInterval(countdown,1000);
function countdown(){
count=count-1
if (count<0){
clearInterval(timer);
return;
}
fun(count)
console.log(count)
}
}
ReactDOM.render(<Countdown/>, document.getElementById('example'));
工作代码此处
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