How to handle errors and set options when acquiring JavaScript location information

When obtaining location information using JavaScript, accurate information may not be obtained or an error may occur. In this article, we will explain how to handle errors and set acquisition options in preparation for such cases.

Please tell me what to do if an error occurs when acquiring location information.

The getCurrentPosition() method allows you to specify a callback function when an error occurs in the second argument. 
You can check the type and cause of the error within this function and perform appropriate error handling.

How to obtain location information

To obtain location information, use JavaScript’s Geolocation API .

The Geolocation API has two methods:

By using these methods, you can obtain the current location information and information when the location information changes.

How to use the getCurrentPosition() method

When using the getCurrentPosition() method , write the code as follows.

navigator.geolocation.getCurrentPosition(successCallback, errorCallback, options);

How to use the watchPosition() method

When using the watchPosition() method , write the code as follows.

var watchId = navigator.geolocation.watchPosition(successCallback, errorCallback, options);

Specify successCallback, errorCallback, and options as arguments, similar to the getCurrentPosition() method . Also, the watchPosition() method returns watchId as a return value because the specified callback function is called every time the position information changes.

How to write a callback function

The callback functions to be passed as successCallback and errorCallback are defined as follows.

function successCallback(position) {
  // Processing using location information
}

function errorCallback(error) {
  // Perform error handling
}

The following objects are passed as arguments for receiving location information.

{
  coords: {
    latitude: Location latitude,
    longitude: Location Longitude,
    accuracy:  Location error (in meters)
  },
  timestamp: Time of location acquisition (UNIX time in milliseconds)
}

The above is the basic method for obtaining location information.

How to handle errors

　An error may occur when obtaining location information using the Geolocation API. For example, if location information is not available or if the user declines to obtain location information. Therefore, proper error handling is important.

The error callback function specified as the second argument of the getCurrentPosition() or watchPosition() method is called when an error occurs. The following arguments are passed to the error callback function:

function errorCallback(error) {
  switch(error.code) {
    case error.PERMISSION_DENIED:
      // What to do when location data acquisition is rejected by the user
      break;
    case error.POSITION_UNAVAILABLE:
      // Processing when location information cannot be obtained
      break;
    case error.TIMEOUT:
      // Processing when location information acquisition times out
      break;
    default:
      // Handling of other errors when they occur
      break;
  }
}

The error.code property has three values:

　Additionally, the Geolocation API has a timeout option that specifies the amount of time before retrying if an error occurs. Specify the timeout option in milliseconds. Default value is Infinity.

var options = {
  timeout: 10000 //  Set timeout to 10 seconds
};
navigator.geolocation.getCurrentPosition(successCallback, errorCallback, options);

The above is the basic method for error handling when acquiring location information.

How to set acquisition options

You can specify options as the third argument to the getCurrentPosition() and watchPosition() methods . Here we will explain the main options.

Below is a sample code that sets the location information retrieval options.

var options = {
  enableHighAccuracy: true,
  maximumAge: 30000, // Use cached information for 30 seconds
  timeout: 10000 // Set timeout to 10 seconds
};
navigator.geolocation.getCurrentPosition(successCallback, errorCallback, options);

In this way, by specifying options to the getCurrentPosition() and watchPosition() methods, you can obtain more appropriate location information. However, please note that depending on the appropriate option settings, battery consumption may increase.

summary

We explained how to set error handling and acquisition options.

By using the Geolocation API, we were able to easily obtain location information.

Location information is one of the important elements essential to the functionality of websites and apps. 
Accurate and secure location information allows us to provide better service to our users. 
However, it is important to consider implementation with user privacy in mind.