返回未定义的函数[重复]

Question

我正在尝试创建一个简单的函数来根据浏览器返回用户位置，但它一直返回未定义：

  function getLocation() {
    //get current location
    var geo_param;
    if(navigator.geolocation) {
      navigator.geolocation.getCurrentPosition(function(position) {
        // Create geolocation parameter
        geo_param = "geolocation=[" + position.coords.latitude + "," + position.coords.longitude + "]";
        console.log(geo_param)
      });
    }
    return geo_param
  }

  function search(activity) {
    var searchUrl = "/s?activity=" + activity + "&" + getLocation()
    window.location.href = searchUrl;
    console.info(searchUrl)
  }

Answer 1

getCurrentPosition 作用域是异步的，所以geo_param 将在 getCurrentPosition 完成运行之前返回。对此的解决方案是使用回调，请参见下面的示例。

 function getLocation(callback, activity) {
     //get current location
     var geo_param;
     if (navigator.geolocation) {
         navigator.geolocation.getCurrentPosition(function (position) {
             // Create geolocation parameter
             geo_param = "geolocation=[" + position.coords.latitude + "," + position.coords.longitude + "]";
             console.log(geo_param);
             callback(geo_param, activity);
         });
     }
 }

 function search(activity) {
     getLocation(search_with_current_location, activity);
 }

 function search_with_current_location(geo_param, activity) {
     var searchUrl = "/s?activity=" + activity + "&" + geo_param;
     window.location.href = searchUrl;
     console.info(searchUrl);
 }

Answer 2

在这种情况下，您的函数在获取响应之前执行。收到API的回复后，需要有回调函数。

另请注意，您在重定向 URL 中没有 query string key geo_param

试试这个：

function getLocation(cb) {
    if (navigator.geolocation) {
        navigator.geolocation.getCurrentPosition(function (position) {
            var geo_param = "geolocation=[" + position.coords.latitude + "," + position.coords.longitude + "]";
            if (typeof cb === 'function') {
                cb(geo_param);
            }
        });
    }
}
function search(activity) {
    getLocation(function (geo_param) {
        window.location.href = "/s?activity=" + activity + "&" + geo_param;
    });
}