Question

I’ve written a bookmarklet which injects an external javascript just before the closing body tag.

The injected script contains two lines:

document.write("");
alert("hello");

The alert works.
The document.write has no effect.

What gives? This should clear the page, but the page remains unchanged.

Answer 1

If you need to overwrite the entire document with an empty string. you need to call document.write in window.onload handler:

window.onload = function(){
   document.write("");
}

When the page is rendering document.write just outputs the string where it is called, but after the page load it replaces the document with the string.

or call document.body.innerHTML = '';