It is possible to override the document.write method. So you can buffer the strings sent to document.write and output the buffer wherever you like. However changing a script from synchronous to asynchronous can cause errors if not handled correctly. Here's an example:
Simplified document.write replacement
(function() {
// WARNING: This is just a simplified example
// to illustrate a problem.
// Do NOT use this code!
var buffer = [];
document.write = function(str) {
// Every time document.write is called push
// the data into buffer. document.write can
// be called from anywhere, so we also need
// a mechanism for multiple positions if
// that's needed.
buffer.push(str);
};
function flushBuffer() {
// Join everything in the buffer to one string and put
// inside the element we want the output.
var output = buffer.join('');
document.getElementById("ad-position-1").innerHTML = output;
}
// Inject the thid-party script dynamically and
// call flushBuffer when the script is loaded
// (and executed).
var script = document.createElement("script");
script.onload = flushBuffer;
script.src = "http://someadserver.com/example.js";
})();
Content of http://someadserver.com/example.js
var flashAdObject = "<object>...</object>";
document.write("<div id='example'></div>");
// Since we buffer the data the getElementById will fail
var example = document.getElementById("example");
example.innerHTML = flashAdObject; // ReferenceError: example is not defined
I've documented the different problems I've encountered when writing and using my document.write replacement: https://github.com/gregersrygg/crapLoader/wiki/What-to-think-about-when-replacing-document.write
But the danger of using a document.write replacement are all the unknown problems that may arise. Some are not even possible to get around.
document.write("<scr"+"ipt src='http://someadserver.com/adLib.js'></scr"+"ipt>");
adLib.doSomething(); // ReferenceError: adLib is not defined
Luckily I haven't come across the above problem in the wild, but that doesn't guarantee it won't happen ;)
Still want to try it out? Try out crapLoader (mine) or writeCapture:
You should also check out friendly iframes. Basically it creates a same-domain iframe and loads everything there instead of in your document. Unfortunately I haven't found any good libraries for handling this yet.
