我是 React 的新手,我正在尝试弄清楚如何洗牌数组。我已经尝试了不同的方法来洗牌数组,但问题始终在于长度。 TypeError: Cannot read property 'length' of undefined
.我不确定为什么会发生这种情况,或者我应该如何在 React 中处理它。对我来说,这不应该是 React 的问题,但我也不知道。当一切正常时会发生什么:
你点击"hard"按钮,它应该渲染数组挑战中的前两个元素,每次你点击这个按钮时,数组都应该被洗牌。
你有什么想法可以帮助我吗?
这是代码:
import React from 'react';
import ReactDOM from 'react-dom';
let era = [
60, 70, 80, 90, 2000
]
let genre = [
'Rock', 'Pop', 'Jazz', 'Country'
]
let challenge = [
'LikeElvis', 'Parent's favourite songs', 'too high for me'
]
class Karaoke extends React.Component {
constructor(props){
super(props);
this.state = {
'easy': '',
'easyChallenge': '',
'hard': '',
'hardChallenge': '',
'hardEra': ''
}
};
selectEasy = () => {
let genreSelected = [];
let challengeSelected = [];
genreSelected.push(genre[Math.floor(Math.random() * genre.length)]);
this.setState({"easy": genreSelected})
challengeSelected.push(challenge[Math.floor(Math.random() * challenge.length)]);
this.setState({"easyChallenge": challengeSelected})
}
selectHard = () => {
let genreSelected = [];
let challengeSelected = [];
let eraSelected = [];
genreSelected.push(genre[Math.floor(Math.random() * genre.length)]);
eraSelected.push(era[Math.floor(Math.random() * era.length)]);
this.setState({ "hard": genreSelected} );
this.setState({ "hardEra": eraSelected} );
this.setState({ "hardChallenge": challengeSelected} );
challengeSelected.push(challenge.slice(0, 2))
console.log(challengeSelected);
}
shuffle = (challenge) => {
let i = challenge.length, temporaryValue, randomIndex;
while (0 !== i) {
randomIndex = Math.floor(Math.random() * i);
i -= 1;
temporaryValue = challenge[i];
challenge[i] = challenge[randomIndex];
challenge[randomIndex] = temporaryValue;
}
return challenge
}
click = () => {
this.selectHard();
this.shuffle();
}
render = () => {
return(
<div>
<button onClick={this.selectEasy}>Easy</button>
<button onClick={this.click}>Hard</button>
<h1>the genre is {this.state.easy} </h1>
<h1>the challenge is {this.state.easyChallenge} </h1>
<h1>Hard mode: {this.state.hard} + {this.state.hardEra + ''s'}</h1>
<h1>Hard mode challenge: {this.state.hardChallenge} </h1>
</div>
)
}
}
ReactDOM.render(<Karaoke />, document.getElementById('root'));
您正在定义需要参数的suffle
方法。但是当你从click
方法调用它时,你没有提供上述参数:
shuffle(challenge) {
// ...
}
click = () => {
// ...
this.shuffle();
}
这将导致声明的参数undefined
,并且 suffle
方法不会默认全局challenge
变量。
要解决此问题,您需要从方法定义中删除参数或在 click
函数中传递它:
shuffle() {
// ...
}
click = () => {
// ...
this.shuffle();
}
/* OR */
shuffle(challenge) {
// ...
}
click = () => {
// ...
this.shuffle(challenge);
}