function loadScript(url, callback,targetWin) {
     if(!targetWin)
    	 targetWin = self;
     var script = targetWin.document.createElement("script")  
     script.type = "text/javascript";  
     if (script.readyState) { // IE  
         script.onreadystatechange = function() {  
             if (script.readyState == "loaded"  
                     || script.readyState == "complete") {  
                 script.onreadystatechange = null;  
                 if(typeof callback == "function")
                	 targetWin.callback();  
             }  
         };  
     } else { // Others  
         script.onload = function() {  
        	 if(typeof callback == "function")
        		 targetWin.callback();    
         };  
     }  
     script.src = url;  
     targetWin.document.getElementsByTagName("head")[0].appendChild(script);  
 } 

//示例
function init(){
	var flexWin = top.frames['flex'];
	var url = "/web/test.js";
	if(window.addEventListener){
		flexWin.addEventListener('load',function(){
			loadScript(url,null,flexWin);
		},false);
	}else if(window.attachEvent){
		window.attachEvent('onload',function(){
			loadScript(url,null,flexWin);
		});
	}else{
		flexWin.onload =function(){
			loadScript('test.js',null,flexWin);
		}
	}
}
/*
* 注意：frame中window对象的获取，需要采用上述形式。
 如果使用 document.getElementsByTagName 或 getElementById 方法，拿到的是一个frame对象，通过该frame对象，我们可以通过 contentWindow来获取对应的window对象。但是，chrome不支持 contentWindow属性。
var frames = top.document.getElementsByTagName("frame");
alert(frames['a1'].contentWindow);//undefined in chrome
*/

//动态加载js、css内容，直接写入页面：

动态添加js/CSS的内容在页面上：
function loadScriptString(code){
    var script = document.createElement("script");
    script.type = "text/javascript";
    try {
        script.appendChild(document.createTextNode(code));
    } catch (ex){  
        script.text = code;  // IE
    }
    document.body.appendChild(script);
}    


function loadStyleString(css){
    var style = document.createElement("style");
    style.type = "text/css";
    try{
        style.appendChild(document.createTextNode(css));
    } catch (ex){
        style.styleSheet.cssText = css; //IE
    }
    var head = document.getElementsByTagName("head")[0];
    head.appendChild(style);
}

Usage:
    loadScriptString('function sayHi(){alert("hi");}');

    loadStyleString('body{background-color:red}');