Question

我对JavaScript的同步/异步处理感到困惑。

我想做的如下。当调用self_driving()时，然后调用get_direction_by_sensor()并使用该方向，电机将由move_to_direction(direction)开始运行。此过程重复5次。

function get_direction_by_sensor(){
  // code for getting direction from sensor
  return direction
};

function move_to_direction(direction){
  direction = get_direction_by_sensor()
  // code for driving motor to the direction
};

function self_driving_loop(maxCount, i) {
  if (i <= maxCount) {
    move_to_direction();
    setTimeout(function(){
      self_driving_loop(maxCount, ++i)
    }, 1000);
  }
};

function self_driving() {
  self_driving_loop(5, 1)
};

所以我希望这段代码像这样运行。

1. get_direction_by_sensor()
1. move_to_direction()
2. get_direction_by_sensor()
2. move_to_direction()
3. get_direction_by_sensor()
3. move_to_direction()
4. get_direction_by_sensor()
4. move_to_direction()
5. get_direction_by_sensor()
5. move_to_direction()

但是实际上它是这样运行的。

1. get_direction_by_sensor()
2. get_direction_by_sensor()
3. get_direction_by_sensor()
4. get_direction_by_sensor()
5. get_direction_by_sensor() // this direction is used for moving
5. move_to_direction()

如何解决此代码？谢谢。

=========详细信息=======

move_to_direction()调用由Python编写的webiopi宏。

function move_to_direction() {
  w().callMacro('get_direction_to_move', [TRIG_F ,ECHO_F ,TRIG_R ,ECHO_R ,TRIG_L ,ECHO_L ,TRIG_B ,ECHO_B], function(macro, args, resp) {
    console.log(resp) // DEBUG
    if(resp == "forward") {
      change_direction('FOWARD');
    } else if(resp == "right") {
      change_direction('RIGHT');
    } else if(resp == "left") {
      change_direction('LEFT');
    } else if(resp == "backward") {
      change_direction('BACKWARD');
    }
  });
}

Answer 1

settimeout必须包装有一个Promise，以便可以等待它。参见

function self_driving_loop(maxCount, i) {
  return new Promise(resolve => {
    if (i <= maxCount) {
       move_to_direction();
       setTimeout(function(){
         self_driving_loop(maxCount, ++i)
         resolve()
       }, 1000);
    }
  })
};

在 async 函数中以这种方式调用

await self_driving_loop(maxCount, i)

Javascript：如何进行同步循环？

1 个答案: