javascript - 类型错误 : Cannot read property 'focus' of null

Question

我有一个如下的 React 组件。当我为以下组件执行测试用例时，尽管在浏览器上我看到生成了元素并且编译中没有错误，但我得到了以下错误。

错误 :

TypeError:无法读取 null 的属性“焦点”

  at Check.componentDidMount (src/components/Payments/Check.js:42:42)
  at node_modules/react-test-renderer/lib/ReactCompositeComponent.js:262:25
  at measureLifeCyclePerf (node_modules/react-test-renderer/lib/ReactCompositeComponent.js:73:12)
  at node_modules/react-test-renderer/lib/ReactCompositeComponent.js:261:11
  at CallbackQueue.notifyAll (node_modules/react-test-renderer/lib/CallbackQueue.js:74:22)
  at ReactTestReconcileTransaction.close (node_modules/react-test-renderer/lib/ReactTestReconcileTransaction.js:34:26)
  at ReactTestReconcileTransaction.closeAll (node_modules/react-test-renderer/lib/Transaction.js:207:25)
  at ReactTestReconcileTransaction.perform (node_modules/react-test-renderer/lib/Transaction.js:154:16)
  at batchedMountComponentIntoNode (node_modules/react-test-renderer/lib/ReactTestMount.js:67:27)
  at ReactDefaultBatchingStrategyTransaction.perform (node_modules/react-test-renderer/lib/Transaction.js:141:20)
  at Object.batchedUpdates (node_modules/react-test-renderer/lib/ReactDefaultBatchingStrategy.js:60:26)

检查.js

export default class Check extends Component {
  static displayName = 'Check';

  static propTypes = {
    check: PropTypes.object,
    translate: PropTypes.func.isRequired,
    countries: PropTypes.object,
    states: PropTypes.object,
    setCheckState: PropTypes.func.isRequired
  };

  onChange = (fieldName, newValue) => {
    let sanitizedFieldName = fieldName.replace('selected', '');
    sanitizedFieldName = sanitizedFieldName.charAt(0).toLowerCase() + sanitizedFieldName.substr(1);
    const newCheckState = {
      ...this.props.check,
      [sanitizedFieldName]: newValue
    };
    this.props.setCheckState(newCheckState, sanitizedFieldName === 'country');
  }

  componentDidMount() {
    document.getElementById('mainHeader').focus();
  }

  render() {
    const { translate, check, countries, states } = this.props;
    const parentType = 'check';
    const stateObj = states[check.country] || { optionArray: [] };

    return (
        <div>
          <div tabIndex="0" id="mainHeader"><h1 {...resolve(CheckStyles, 'mainHeader')}>
            {translate('PanelPaymentsCheckHeaderText')}
          </h1></div>
          <div {...resolve(CheckStyles, 'bankInfoContainer')}>
            <h3 {...resolve(CheckStyles, 'bankAccountHeader')}>
              {translate('PanelPaymentsCheckSubHeaderText')}
            </h3>
            ........
            ........                
          </div>
        </div>
    );
  }
}

Answer 1

我添加了空检查以消除错误。这是一个愚蠢的解决方案。

componentDidMount() {
  if(this.refs.mainHeader){
  this.refs.mainHeader.focus();
   }
}