Question

我有这个vue2代码：

checkUser2() {
    var returnValue;
    axios.get(`api/users/CheckUsername/${this.username}`)
          .then(response => {
              returnValue = response.data.error === 0;
          }, errorCallBack => {
              returnValue = false;
          });
    return returnValue;
}

我称之为：

var a = this.checkUser2();
console.log(a);

并且它总是返回undefined。我做错了什么？

Answer 1

如果要从此方法返回值，则必须从函数返回 promise 并使用回调来成功捕获结果。

@Component
@DisallowConcurrentExecution
public class Job1 implements Job {

private final Logger log = LoggerFactory.getLogger(this.getClass());

@Value("${schedule}")
private String frequency;

@Autowired
private Service service;

@Override
public void execute(JobExecutionContext jobExecutionContext) {
    log.info("execute");
}

@Bean(name = "jobBean1")
public JobDetailFactoryBean job() {
    return SchedulerConfig.createJobDetail(this.getClass());
}

@Bean(name = "jobBean1Trigger")
public CronTriggerFactoryBean jobTrigger(@Qualifier("jobBean1")JobDetail jobDetail) {
    return SchedulerConfig.createCronTrigger(jobDetail, frequency);
}

当你打电话时：

@Component
@DisallowConcurrentExecution
public class Job2 implements Job {

private final Logger log = LoggerFactory.getLogger(this.getClass());

@Value("${schedule}")
private String frequency;

@Autowired
private Service service;

@Override
public void execute(JobExecutionContext jobExecutionContext) {
    log.info("execute");
}

@Bean(name = "jobBean2")
public JobDetailFactoryBean job() {
    return SchedulerConfig.createJobDetail(this.getClass());
}

@Bean(name = "jobBean2Trigger")
public CronTriggerFactoryBean jobTrigger(@Qualifier("jobBean2")JobDetail jobDetail) {
    return SchedulerConfig.createCronTrigger(jobDetail, frequency);
}

Answer 2

我对vue2一无所知，但我知道axios对promises有效，所以因为你在你的诺言之外返回returnValue，你的函数返回{{1}的当前值}，这是returnValue。

Answer 3

这是因为您在请求发出之前返回了值。你需要制作一个Promise，当它结算时，返回值。

checkUser2() {
  return new Promise((resolve, reject) => {

    var returnValue;
    axios.get(`api/users/CheckUsername/${this.username}`)
    .then(response => {
      returnValue = response.data.error === 0;
      resolve(returnValue);
    }, errorCallBack => {
      returnValue = false;
      reject(returnValue);
    });
  });
}

然后你只需要像这样调用它来获取值：

this.checkUser2().then(val => {
 a = val;
})

希望这会对你有所帮助。

Javascript函数总是返回undefined

3 个答案: