js替换元素与设置时间间隔

var lastReportTime = 0;

//设置时间间隔
window.onload = function(){
    setInterval(handleRefresh, 3000);
}

function handleRefresh(){
    var url = "http://gumball.wickedlysmart.com" +
        "?callback=updateSales" +
        "&lastreporttime=" + lastReportTime +
        "&random=" + (new Date()).getTime();
    var newScriptElement = document.createElement("script");
    newScriptElement.setAttribute("src", url);
    newScriptElement.setAttribute("id","jsonp");

    var oldScriptElement = document.getElementById("jsonp");
    var head = document.getElementsByTagName("head")[0];
    if (oldScriptElement == null){
        head.appendChild(newScriptElement)
    } else {
        //替换元素
        head.replaceChild(newScriptElement, oldScriptElement);
    }
}

function updateSales(sales){
    var salesDiv = document.getElementById("sales");
    for (var i = 0; i < sales.length; i++){
        var sale = sales[i];
        var div = document.createElement("div");
        div.setAttribute("class", "saleItem");
        div.innerHTML = sale.name + " sold " + sale.sales + " gumballs";
        salesDiv.appendChild(div);
    }
    if (sales.length > 0){
        lastReportTime = sales[sales.length - 1].time;
    }

}