JavaScript/jQuery string handling

Question

Recently I wrote some code to take two arrays of data and create a title. Each array could have 0-n elements. However, the multiple if statements seem messy to me. Is there a nicer way to do this? Perhaps one that harnesses the power of jQuery better?

var campaign_names = data["campaign_names"];
var list_names = data["list_names"];
var title;

if (campaign_names && campaign_names.length > 1) {
  campaign_names = campaign_names.join(", ");
} else if (campaign_names) {
  campaign_names = campaign_names[0];
}

if (list_names && list_names.length > 1) {
  list_names = list_names.join(", ");
} else if (list_names) {
  list_names = list_names[0];
}

if (campaign_names && list_names) {
  title = campaign_names + " & " + list_names;
} else if (campaign_names) {
  title = campaign_names; 
} else if (list_names) {
  title = list_names;
}

Answer 1

Fun question,

if (campaign_names && campaign_names.length > 1) {
  campaign_names = campaign_names.join(", ");
} else if (campaign_names) {
  campaign_names = campaign_names[0];
}

is equivalent to

if (campaign_names && campaign_names.length ) {
  campaign_names = campaign_names.join(", ");
}

if you initialized campaign_names and list_names to '' you could simplify the last part to

if (campaign_names && list_names) {
  title = campaign_names + " & " + list_names;
} else {
  title = campaign_names + list_names; 
}

Personally I would go for this:

var campaigns = data["campaign_names"] || [],
    lists = data["list_names"] || [],
    title;

if (campaigns.length) {
  campaigns = campaigns .join(", ");
}

if (lists.length) {
  lists = lists.join(", ");
}

if (campaigns && lists) {
  title = campaigns + " & " + lists;
} else {
  title = campaigns + lists;
}

If I was feeling ternary that day I would write the last part as

  title = campaigns + (campaigns&&lists) ? " & " : "" + lists;

Answer 2

Leveraging @konjin's code, I might use an array of property names to make it easy to add/remove them without affecting the code.

var propertyList = [ "campaign_names", "list_names" ],
    tempList = [ ],
    tempTitle = '',
    title = '';

for( var i=0; i<propertyNames.length; ++i ) {
    tempList = data[ propertyNames[i] ] || [ ];
    tempTitle = tempList.join(", ");
    title = title + (title && tempTitle) ? " & " : "" + tempTitle;
}