Javascript使用承诺等待条件为true

你必须这么做 return

function waitForCondition(conditionObj) {
  return new Promise(resolve => {
    var start_time = Date.now();
    function checkFlag() {
      if (conditionObj.arg == conditionObj.test) {
        console.log('met');
        resolve();
      } else if (Date.now() > start_time + 3000) {
        console.log('not met, time out');
        resolve();
      } else {
        window.setTimeout(checkFlag, 1000); 
      }
    }
    checkFlag();
  });
}

async function run() {
  console.log('before');
  await waitForCondition({arg: '1', test: '1'})
  console.log('after');
}
run();

我对你的代码进行了一些重构。要获取当前时间,请使用 Date.now() .你应该可以打电话 resolve 没有1毫秒的超时。

我相信你真正想要的是

function waitForCondition(conditionObj) {
  var start_time = new Date().getTime()

  async function checkFlag() {
    if (conditionObj.arg == conditionObj.test) {
      console.log('met');
       // return something?
    } else if (new Date() > start_time + 3000) {
      console.log('not met, time out');
      // throw some error?
    } else {
      await new Promise(resolve => setTimeout(resolve, 1000));
      return checkFlag();
    }
  }
  return checkFlag();
}

或者用循环代替递归

async function waitForCondition(conditionObj) {
  var start_time = new Date().getTime()

  while (true) {
    if (conditionObj.arg == conditionObj.test) {
      console.log('met');
      break; // or return
    }
    if (new Date() > start_time + 3000) {
      console.log('not met, time out');
      break; // or throw
    }
    await new Promise(resolve => setTimeout(resolve, 1000));
  }
}

waitForCondition 隐式返回 undefined .尝试在末尾添加一个返回语句:

return checkFlag();

正如评论中提到的,有一个条件 checkFlag() 未定义 您可能希望通过返回 Promise .