Delete http get url (+ angular2 http get)

[meansoup]

hey guys.
I want to using angular2’s http. and I make sample code for checking return value.

getData(suburl){

let url = '115.68.xxx.xxx' + suburl;

return this.http.get(url).toPromise()
         .then(response => response.json())
         .catch(this.handleError);

}

these are my code for http get, (I do not really know it works)
and i use url with suburl for my hosting server (i can check server with browser and it works correctly)
but it shows like this (when i user ionic run browser)

now i want adjust my question.

1. can i delete localhost from url? like http://115.68.xxx.xxx
2. these http.get code is right? how can i use?
3. additionally, what ‘.then’ works? in other example some people use ‘.map’, I just thought it makes json but didn’t understand.
4. additionally, .catch like JAVA code’s try, catch??

thanks for reading long question.