Unable to get property 'createRange' of undefined when loading the page

function getRange(editor) {
if (ie) return getSelection(editor).createRange();
return getSelection(editor).getRangeAt(0);
}

// getSelection - gets the current text range object
function getSelection(editor) {
if (ie) return editor.doc.selection;
return editor.$frame[0].contentWindow.getSelection();
}