Set HTML element content from URL

gistfile1.txt

function setContentFromUrl(url, container, opt){
        console.log("loading", url, "into", container);
        opt = opt || {};
        var data_filter = opt.filter;
        var err_handler = opt.err_handler;
        var xhr= new XMLHttpRequest();
        xhr.open('GET', url, true);
        xhr.onreadystatechange= function() {
                if (this.readyState!==4) return;
                if (this.status!==200){
                        err_handler(this.status);
                        return;
                }
                console.log("Have data");
                var data = this.responseText;
                if (data_filter){
                        data = data_filter(data);
                }
                var tagName = container.tagName.toLowerCase();
                switch(tagName){
                case "pre":
                case "span":
                case "div": container.innerText = data; break;
                case "textarea": container.value = this.data; break;
                default: throw new Error("Unsupported container type: "+tagName);
                }
        };
        xhr.send();
}