Q: Injecting Html code in a dynamic Web Page I need to inject some Html code into web pages that launch in browser.
Is there any way to do it?

For example: I need to add a button dynamically at the bottom of a web page at load event
  of a web site.

Is it possible to do this?

A: You can add html code using javaScript.
document.getElementById("your div id name here").innerHTML = "<button>TEST</button>";

To have it execute when your page is loaded you can put it into a function and have it executed onload:
function addButton() {
    document.getElementById("your div id name here").innerHTML = "<button>TEST</button>";
}

and call your function onload like this in your html body tag:
<body onload="addButton()">

