Javascript AJAX include file witth eval

问题:

Suppose I have

1) a HTML document.

2) This HTML document loads Javascript file "code.js" like this:

<script src="code.js">

3) User clicks button which runs "fetchdata" function in "code.js",

4) "fetchdata" function looks like this:

var xmlhttp = new XMLHttpRequest();
xmlhttp.onreadystatechange = function() {
    if (xmlhttp.readyState==4) {
        myjsdata = xmlhttp.responseText;
    }
}
xmlhttp.open("GET", 'http://www.example.com/data.js', false);
xmlhttp.send(null);

...

Now how do I do the following successfully:

I want to insert/eval my Javascript in a way, so all functions in "code.js" including "fetchdata" and functions defined above/below can access the data (structures, declarations, pre-calculated data values etc.) in "data.js".

(If this was possible, it would be idea since I could wait loading the actual JS data file until the user explicitly requests it.)

回答1:

jQuery always has something for everything:

http://api.jquery.com/jQuery.getScript/

Loads a javascript file from url and executes it in the global context.

edit: Oops, didn't see that you weren't using jQuery. Everyone is always using jQuery...

Just do:

var scrpt = document.createElement('script');
scrpt.src='http://www.example.com/data.js';
document.head.appendChild(scrpt);

回答2:

i think you should take a look at this site

this site talks about dynamic loading and callbacks (with examples) - where you can call a function in the loaded script after it loads. no jQUery, just pure JS.

回答3:

This depends on a lot of factors, but in most cases, you will want to load all of your code/html/css in one sitting. It takes fewer requests, and thus boast a higher perceived performance benefit. Unless your code file is over several Megabytes big, loading it when a user requests it is unnecessary.

In addition to all of this, modifying innerHTML and running scripts via eval can be very cumbersome and risky (respectively). Many online references will back this point. Don't assume that, just because a library is doing something like this, it is safe to perform.

That said, it is entirely possible to load external js files and execute them. One way is to stick all of the code into a newly created script tag. You can also just try running the code in an eval function call (though it isn't recommended).

address = "testscript.js";

var req = (window.XMLHttpRequest)?new XMLHttpRequest():new ActiveXObject("Microsoft.XMLHTTP");
if(req == null) {
    console.log("Error: XMLHttpRequest failed to initiate.");
}
req.onload = function() {
    try {
        eval(req.responseText);
    } catch(e) {
        console.log("There was an error in the script file.");
    }
}
try {

    req.open("GET", address, true);
    req.send(null);

} catch(e) {
    console.log("Error retrieving data httpReq. Some browsers only accept cross-domain request with HTTP.");
}