When you create a new window using open, it returns a reference to the new window, you can use that reference to write to the newly opened window via its document object.
Here is an example:
var newWin = open('url','windowName','height=300,width=300');
newWin.document.write('html to write...');
I would not recomend you to use document.write as others suggest, because if you will open such window twice your HTML will be duplicated 2 times (or more).
Use innerHTML instead
var win = window.open("", "Title", "toolbar=no,location=no,directories=no,status=no,menubar=no,scrollbars=yes,resizable=yes,width=780,height=200,top="+(screen.height-400)+",left="+(screen.width-840));
win.document.body.innerHTML = "HTML";
You can open a new popup window by following code:
var myWindow = window.open("", "newWindow", "width=500,height=700");
//window.open('url','name','specs');
Afterwards, you can add HTML using both myWindow.document.write(); or myWindow.document.body.innerHTML = "HTML";
What I will recommend is that first you create a new html file with any name.
In this example I am using
newFile.html
And make sure to add all content in that file such as bootstrap cdn or jquery, means all the links and scripts. Then make a div with some id or use your body and give that a id. in this example I have given id="mainBody" to my newFile.html <body> tag
<body id="mainBody">
Then open this file using
<script>
var myWindow = window.open("newFile.html", "newWindow", "width=500,height=700");
</script>
And add whatever you want to add in your body tag. using following code