我有一个脚本,知道要加载包含
javascript类的动态脚本.
我正在使用以下代码加载类脚本：
我正在使用以下代码加载类脚本：
var head = document.getElementsByTagName("head")[0];
var script = document.createElement("script");
script.type = "text/javascript";
script.src = "myscript.js";
head.appendChild(script);
然后我尝试使用eval创建新类：
var classObj = eval(" new MyClass()" );
问题是eval的代码正在被执行bofre脚本已经加载到内存中,我收到一个MyClass未定义的错误.
有没有办法同步这些事件？我需要确保脚本完全加载到内存中,然后才能开始分配类.
解决方法
您需要将一个事件处理程序附加到onload方法,符合Web标准的浏览器或onreadystatechange中,检查在Internet Explorer中的script.readyState属性是否等于“已加载”或“完成”.
在通知脚本被加载之前,您可能正在尝试访问尚未声明或创建的对象,函数和属性.
这是一个示例函数,从我的Javascript library,bezen.org中的模块bezen.dom.js中提取：
var appendScript = function(parent,scriptElt,listener) {
// append a script element as last child in parent and configure
// provided listener function for the script load event
//
// params:
// parent - (DOM element) (!nil) the parent node to append the script to
// scriptElt - (DOM element) (!nil) a new script element
// listener - (function) (!nil) listener function for script load event
//
// Notes:
// - in IE,the load event is simulated by setting an intermediate
// listener to onreadystate which filters events and fires the
// callback just once when the state is "loaded" or "complete"
//
// - Opera supports both readyState and onload,but does not behave in
// the exact same way as IE for readyState,e.g. "loaded" may be
// reached before the script runs.
var safelistener = catchError(listener,'script.onload');
// Opera has readyState too,but does not behave in a consistent way
if (scriptElt.readyState && scriptElt.onload!==null) {
// IE only (onload===undefined) not Opera (onload===null)
scriptElt.onreadystatechange = function() {
if ( scriptElt.readyState === "loaded" ||
scriptElt.readyState === "complete" ) {
// Avoid memory leaks (and duplicate call to callback) in IE
scriptElt.onreadystatechange = null;
safelistener();
}
};
} else {
// other browsers (DOM Level 0)
scriptElt.onload = safelistener;
}
parent.appendChild( scriptElt );
};
要适应您的需要,您可以将调用替换为catchError,该函数将侦听器包装以捕获和记录错误,并使用修改的函数：
var appendScript = function(parent,e.g. "loaded" may be
// reached before the script runs.
var safelistener = function(){
try {
listener();
} catch(e) {
// do something with the error
}
};
// Opera has readyState too,but does not behave in a consistent way
if (scriptElt.readyState && scriptElt.onload!==null) {
// IE only (onload===undefined) not Opera (onload===null)
scriptElt.onreadystatechange = function() {
if ( scriptElt.readyState === "loaded" ||
scriptElt.readyState === "complete" ) {
// Avoid memory leaks (and duplicate call to callback) in IE
scriptElt.onreadystatechange = null;
safelistener();
}
};
} else {
// other browsers (DOM Level 0)
scriptElt.onload = safelistener;
}
parent.appendChild( scriptElt );
};
