Get data on firebase database to replace string

When i Run this function to get data from firebase database

function gotData(data){
    var url_sitemap = data.val();
    var keys = Object.keys(url_sitemap);
    console.log(keys);
}

Results is

[ 'key1', 'key2', 'key3', 'key4' ]

I need add data to this 'page-xx/' on below

var sitemap = sm.createSitemap({ 
    hostname: 'xxx.com',
    urls: [
        { url: '/page-xx/},
        { url: '/page-xx/},
        { url: '/page-xx/},
        { url: '/page-xx/}
    ]
});

How can i replace /page-xx/ with data on database?

via Moomoo Soso