PDF Output: Enable using javascript inside header and footer templates

manual/conversion.rst

@@ -840,7 +840,7 @@ template::
 This will display the title at the left and the author at the right, in a font
 size smaller than the main text.
 
-Finally, you can also use the current section in templates, as shown below::
+You can also use the current section in templates, as shown below::
 
     <p style="text-align:right">_SECTION_</p>
 
@@ -850,6 +850,12 @@ Outline). If the document has no table of contents then it will be replaced by
 empty text. If a single PDF page has multiple sections, the first section on
 the page will be used.
 
+You can even use javascript inside the header and footer templates, for
+example, the following template will cause page numbers to start at 4 instead
+of 1::
+
+    <p id="pagenum" style="text-align:center;"></p><script>document.getElementById("pagenum").innerHTML = "" + (_PAGENUM_ + 3)</script>
+
 .. note:: When adding headers and footers make sure you set the page top and
     bottom margins to large enough values, under the Page Setup section of the
     conversion dialog.

src/calibre/ebooks/oeb/display/paged.coffee

@@ -8,6 +8,10 @@
 
 log = window.calibre_utils.log
 
+runscripts = (parent) ->
+    for script in parent.getElementsByTagName('script')
+        eval(script.text || script.textContent || script.innerHTML || '')
+
 class PagedDisplay
     # This class is a namespace to expose functions via the
     # window.paged_display object. The most important functions are:
@@ -238,8 +242,10 @@ class PagedDisplay
             section = py_bridge.section()
         if this.header != null
             this.header.innerHTML = this.header_template.replace(/_PAGENUM_/g, pagenum+"").replace(/_TITLE_/g, title+"").replace(/_AUTHOR_/g, author+"").replace(/_SECTION_/g, section+"")
+            runscripts(this.header)
         if this.footer != null
             this.footer.innerHTML = this.footer_template.replace(/_PAGENUM_/g, pagenum+"").replace(/_TITLE_/g, title+"").replace(/_AUTHOR_/g, author+"").replace(/_SECTION_/g, section+"")
+            runscripts(this.footer)
 
     fit_images: () ->
         # Ensure no images are wider than the available width in a column. Note