Baidu Maps API Geolocation: Get User's Current Location

This code snippet is using the Baidu Maps API to get the user's current geolocation. \n\n1. It creates a new instance of the `BMap.Geolocation` object.\n2. It calls the `getCurrentPosition` method of the geolocation object, passing in a callback function.\n3. Inside the callback function, it checks if the geolocation result is available (`res` is not null or undefined).\n4. If the result is available, it extracts the longitude (`lng`) and latitude (`lat`) from the `point` property of the result object.\n5. It also extracts the province, city, district, street, and street number from the `address` property.\n6. It assigns the longitude and latitude values to the `center` variable.\n7. If the geolocation result is not available, it assigns a default longitude and latitude (115.44892, 38.9183) to the `center` variable.