javascript - 从异步表达式中获取返回值

Question

如何从以下代码中获取返回值？我不想只是控制台记录它

function get_disk_space(callback){
    checkDiskSpace('C:\\').then((diskSpace) => {
      var free = Math.floor(diskSpace.free/1000000000)
      var size = Math.floor(diskSpace.size/1000000000)
      var used = size - free
      percent = (size - free)
      percent = percent/size*100
      percent = Math.floor(percent)+'%'
      return percent;
    });
  }

运行此命令将返回未定义，而在返回百分比之前运行控制台日志将给我正确的答案..

Answer 1

您可以简单地添加一个 then 处理程序来处理解析的值，例如:

function get_disk_space(callback) {
    return checkDiskSpace('C:\\').then((diskSpace) => {
        var free = Math.floor(diskSpace.free / 1000000000)
        var size = Math.floor(diskSpace.size / 1000000000)
        var used = size - free
        percent = (size - free)
        percent = percent / size * 100
        percent = Math.floor(percent) + '%'
        return percent;
    });
}

为了访问 get_disk_space 函数范围之外的结果，您需要执行以下操作:

get_disk_space().then((result) => {
   //log and handle your result
   console.log(result);
   // handle your result
});

如果您调用 get_disk_space 的函数是异步的，您可以简单地执行以下操作:

async function testFunc() {
const result = await get_disk_space();
// handle result
}