function checkAll(bx) {
var cbs = document.getElementsByTagName('input');
for(var i=0; i < cbs.length; i++) {
if(cbs[i].type == 'checkbox') {
cbs[i].checked = bx.checked;
}
}
}
Have that function be called from the onclick attribute of your checkbox to check all
<input type="checkbox" onclick="checkAll(this)">
Edit I misread your question a little, i see you have attempted it in your code. the getElementsByTagName has to be plural which you may have typo'd there and has to be a tag as specified by the answer above
Edit: Passing the master checkbox as a parameter would allow for toggling check/uncheck as suggested by vol7ron and has been modified in this answer appropriately.
The question asks for all checkboxes on the page so this would suffice.
However, providing control of which elements to look for checkboxes can be achieved in may ways, too many to go into detail but examples could be document.getElementById(id).getElementsByTagName if all checkboxes to be controlled are branched nodes from one element.
Otherwise, you can iterate through a further tag name retrieval / custom class name retrieval to name a few.
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