[removed] style.display:'block' doesn't work

Question

any idea why this JavaScript just shows \"block\" and not the content of the (hidden) DIV?

Answer 1

The value of the javascript expression

document.getElementById('mydiv').style.display='block'

is the string 'block' - think of the way you can do a=b='something' - in javascript the value of an assignment expression is the assigned value.

If you try

link

You'll find clicking the link navigates to a document containing just the word howdy - and the same thing is happening with your code. You can stop this happening by adding an explicit void(0), or by wrapping the code in an immediately-invoked function expression that doesn't return a value (i.e. implicitly returns undefined), so:

(This structure is commonly used in bookmarklets). However, as several comments have already pointed out, in general the use of javascript: hrefs is frowned upon, and you should consider using event handling instead.