var num = langs.size();
selectAll.change(function(event){
    var checked = event.target.checked;
    langs.prop('checked',checked);
    selectAllLabel.toggle(!checked);
    deselectAllLabel.toggle(checked);
});
invertSelect.click(function(){
    langs.map(function(index,domEle){
        domEle.checked = !domEle.checked;
    });
    check();
});
function check(){
    var checkedNum = 0;
    langs.map(function(index,domEle){
        if(domEle.checked){
            checkedNum++;
        }
    });
    if(checkedNum === num){
        deselectAllLabel.show();
        selectAllLabel.hide();
        selectAll.prop('checked',true);
    }else{
        selectAllLabel.show();
        deselectAllLabel.hide();
        selectAll.prop('checked',false);
    }
}
langs.change(function(){
    check();
});