Nested ifs to test if one or both of two conditions is true

Question

I have an object, data, that may or may not contain the members site_with_same_coords and/or site_with_same_name. I test for these and if one or both exist, I alerts to the user:

if (data.site_with_same_coords){
    var SameCoordsExists = true;
    same_coords_message = 'The site ';
    same_coords_message += data.site_with_same_coords.name;
    same_coords_message += 'already already exists in the location you have indicated';
}

if (data.site_with_same_name){
    var SameNameExists = true;
    same_name_message = 'The site ';
    same_name_message += data.site_with_same_name.name;
    same_name_message += 'already already exists in a differnt location from the one you have indicated';
}

if (SameCoordsExists && SameNameExists){
    if(data.site_with_same_name.id != data.site_with_same_coords.id){
        alert(same_coords_message + '\n' + same_name_message);
    }else if (SameCoordsExists){
        alert(same_coords_message);
    }
    }else if (SameNameExists){
        alert(same_name_message);
    }
}

Is there a better way of doing this?

Answer 1

Sure, you could put them in an array and join them:

var messages = [];

if(data.site_with_same_coords) {
    messages.push('The site ' + data.site_with_same_coords.name + ' already exists in the location you have indicated');
}

if(data.site_with_same_name && !(data.site_with_same_coords && data.site_with_same_name.id === data.site_with_same_coords.id)) {
    messages.push('The site ' + data.site_with_same_name.name + ' already exists in a different location from the one you have indicated');
}

alert(messages.join('\n'));

Also, wouldn't the user be a bit confused if they received the message:

The site some_site already exists in the location you have indicated
The site some_other_site already exists in a different location from the one you have indicated

? Just a thought.

Answer 2

This skeleton:

if (A && B) {
  if (C)
    print(msgA);
  print(msgB);
} else {
  print(msgA);
}

can be rewritten like this:

var AB = A && B;
if ((AB && C) || !AB)
  print(msgA);
if (AB)
  print(msgB);

as you can see, msgA and msgB appear only once, so you can create the strings on the fly right where they're printed. Obviously, in your case, A would be data.site_with_same_coords, B would be data.site_with_same_name and C would be data.site_with_same_name.id != data.site_with_same_coords.id.

It goes without saying that the rewritten version is much less readable.

update: if you really need to alert() then you'd do:

var AB = A && B;
if ((AB && C) || !AB)
  msg += msgA;
if (AB)
  msg += msgB;
if (msg)
  alert(msg);