// tab_selected var stores the last clicked tab
// which will be toggled when another is clicked
var tab_selected = 'tab_one';

function select(id) {
    var old_tab = document.getElementById(tab_selected);
	// toggle the previously selected tab if necessary
    if (old_tab != null) {
        // toggle tab
        var old_div = document.getElementById('selected_' + tab_selected);
        old_tab.className = '';
        old_div.style.display = 'none';
	}

	if (tab_selected != id || tab_selected == id) {
		tab_selected = id;
		var tab_el = document.getElementById(id);
		var div_el = document.getElementById('selected_' + id);

        tab_el.className = 'selected';
		div_el.style.display = 'block';
	} else {
        tab_selected = null;
	}
}