Question

Why the following code generates TypeError: document.getElementById("docPrint") is null

var printwindow = window.open('', '', 'fullScreen=no');
printwindow.document.write('<iframe id="docPrint" width="100%" height="100%" src="http://localhost:8080/hiring/docs/Keneth _1340800082258/Keneth _resume_1340800082258.pdf"></iframe>');
printwindow.self.focus();
document.getElementById('docPrint').focus();
document.getElementById('docPrint').contentWindow.print();

Answer 1

You need to prefix your calls to document.getElementById with ‘printwindow’:

printwindow.document.getElementById('docPrint').focus();
printwindow.document.getElementById('docPrint').contentWindow.print();

You might also want to keep a reference to the element in a variable, to avoid the boilerplate

var el = printwindow.document.getElementById('docPrint');
el.focus();
el.contentWindow.print();