Javascript debut - from Chrome console to a bookmarklet

Question

I am new to JS and am trying to write a simple bookmarklet for a website that has divs with class "collapseable" set to display: none; I want by one click to set all elements with class "collapseable" to display: block. Browsing this website, I managed to put together the following code, which works fine when I paste it in Google Chrome's JS console: it returns the value "block" but the effect on the website is the one I seek. However, when I create a bookmarklet with URL javascript:mycode... , it only brings up a blank page with the text "block".

Here is my code, I would very much appreciate if somebody could tell me what I'm doing wrong:

javascript:function getElementsByClassName(classname, node)  {
    if(!node) node = document.getElementsByTagName("body")[0];
    var a = [];
    var re = new RegExp('\\b' + classname + '\\b');
    var els = node.getElementsByTagName("*");
    for(var i=0,j=els.length; i<j; i++)
    if(re.test(els[i].className))a.push(els[i]);
    return a;};
var elems = getElementsByClassName('collapseable');
for (var i=0;i<elems.length;i+=1){
   elems[i].style.display = 'block';}

Answer 1

When I tried making a bookmarklet myself, I had the same problem. My solution was to use void (function({ /* your code */ })() .

javascript:void(function(){
    var getElsByCN = document.getElementsByClassName ||
        function(classname, node)  {
            if(!node) node = document.body;
            var a = [],
                re = new RegExp('\\b' + classname + '\\b'),
                els = node.getElementsByTagName("*");
            for (var i = 0, j = els.length; i < j; i++)
                if (re.test(els[i].className))
                    a.push(els[i]);
            return a;
        };
    var elems = getElsByCN('collapseable');
    for (var i = 0; i < elems.length; i++)
       elems[i].style.display = 'block';
)();

This works because it returns an undefined value due to the use of void . When your script wrote block on the page, it was likely because that was the last value set/accessed by the funtion.