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();

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();

• javascript
• document
• getelementbyid

• 4 Did you consider that the element of id docPrint does not exist? Because that is most likely what it is. – David G Commented Jul 11, 2012 at 11:49

3 Answers 3

You are operating across two windows.

printwindow.document.write
document.getElementById

If you want to get the element you created in the popup then you have to call it's gEBI method.

printwindow.document.write
printwindow.document.getElementById

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();

Prependprintwindow. to each instance of document.getElementById:

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