Sharepoint 2013 get absolute URL of List using JavaScript

For Document library:

Just append the _spPageContextInfo.siteAbsoluteUrl as shown below code to get absolute url of the list.

function result() {
    var listID   = list.get_id();
    var listName = list.get_title();
    var listURL  = listRootFolder.get_serverRelativeUrl();
    var absUrl = _spPageContextInfo.siteAbsoluteUrl +"/"+ listURL; //absUrl is now absolute url of the list.
}

For List:

Just append the _spPageContextInfo.webAbsoluteUrl as shown below code to get absolute url of the list. Just update methods as shown below.

function init() {

    //load site
    var currentcontext = new SP.ClientContext('/StrategicProjectOffice');
    list = currentcontext.get_web().get_lists().getByTitle('Test List');
    listRootFolder = list.get_rootFolder();
    web = currentcontext.get_web();

    currentcontext.load(list, 'Title', 'Id');
    currentcontext.load(web);
    currentcontext.load(listRootFolder);
    currentcontext.executeQueryAsync(Function.createDelegate(this, result), Function.createDelegate(this, oncListQueryFailed));
}

function result() {
    var listID   = list.get_id();
    var listName = list.get_title();
    var listURL  = listRootFolder.get_serverRelativeUrl();
    var absUrl = web.get_url() + "/Lists/" + listRootFolder.get_name(); //absUrl is now absolute url of the list.
}

You can make use of the _spPageContextInfo to create a full url. I couldnt find a specific method, so i modified your code as below. This is will work for Lists only, for document library you need to remove /Lists/ from the code. Not necessarily the best approach, but works as expected.

var list;
var listRootFolder;
ExecuteOrDelayUntilScriptLoaded(init, "sp.js");

function init() {

    //load site
    var currentcontext = new SP.ClientContext('/StrategicProjectOffice');
    list = currentcontext.get_web().get_lists().getByTitle('Test List');
    listRootFolder = list.get_rootFolder();

    currentcontext.load(list, 'Title', 'Id');
    currentcontext.load(listRootFolder);
    currentcontext.executeQueryAsync(Function.createDelegate(this, result), Function.createDelegate(this, oncListQueryFailed));
}

function result() {
    var listID   = list.get_id();
    var listName = list.get_title();
    var listURL  = listRootFolder.get_serverRelativeUrl();
    console.log(listURL);

    var fullUrl = _spPageContextInfo.webAbsoluteUrl + "/Lists/" + listRootFolder.get_name();
    console.log(fullUrl);
}

function oncListQueryFailed(sender, args) {
    alert('Request failed. ' + args.get_message() + '\n' + args.get_stackTrace());
}