N久前写的一个JSONP请求方法

function getJSON(url, params, callback, charset){    
    var w = window,
        query = url.indexOf("?") == -1 ? "?" : "&",
        head,
        callback = isFunction(params) ? params : callback,
        charset = charset || "utf-8"
    function getTimeVer(){
        return new Date().getTime();
    }
    
    function isFunction(obj){
        return Object.prototype.toString.call(obj) === "[object Function]";
    }
    
    function load(url){
        var script = document.createElement('script'),
            done = false;
        script.src = url;
        script.async = true;
        script.charset = charset;
 
        script.onload = script.onreadystatechange = function() {
            if ( !done && (!this.readyState || this.readyState === "loaded" || this.readyState === "complete") ) {
                done = true;
                script.onload = script.onreadystatechange = null;
                if ( script && script.parentNode ) {
                    script.parentNode.removeChild( script );
                }
            }
        };
        if ( !head ) {
            head = document.getElementsByTagName('head')[0];
        }
        head.appendChild( script );        
    }
    
    if(typeof params === "string"){
        params = params || "";
        query += "&";
    }else{
        params = params || {};
        for (var key in params ) {
            if ( params.hasOwnProperty(key) ) {
                query += encodeURIComponent(key) + "=" + encodeURIComponent(params[key]) + "&";
            }
        }
    }
    var jsonVar = "jsonp" + getTimeVer();
    w[jsonVar] = function(data){
        callback.call(null, data);
        try{
            delete w[jsonVar];
        }catch(e){
            
        }
        w[jsonVar] = null;
    };
    
    load(url + query + "callback=" + jsonVar);
    
}

document.getElementById("click").onclick = function(){
    getJSON("http://www-0f3d8c090ce:8080/foundation/servlet/JsonCallBack", function(data){
        alert(data.name);
    });
};