javascript - 类型错误 : Cannot read property 'map' of undefined on React. js

Question

我正在按照有关受控输入的 React.js 在线教程进行操作，但我反复收到错误

TypeError: Cannot read property 'map' of undefined

import CallRow from "./CallRow";
import React from "react";

class SearchPage extends React.Component {
  constructor() {
    super();
    this.state = {
      search: "Level Up"
    };
  }

  updateSearch(event) {
    this.setState({ search: event.target.value.substr(0, 20) });
  }

  render() {
    return (
      <div>
        <ul>
          {this.props.calls.map(call => (
            <CallRow call={call} key={call.id} />
          ))}
        </ul>
        <input
          type="text"
          value={this.state.search}
          onChange={this.updateSearch.bind(this)}
        />
      </div>
    );
  }
}

export default SearchPage;

Answer 1

好像是call prop undefined.

在映射 prop 值之前，检查它是否未定义。

请引用以下代码:

<ul>
    {(this.props.calls || []).map(call => (
        <CallRow call={call} key={call.id} />
    ))}
</ul>