Mark / Uncheck Checkbox from a button

Test like this:

function marcardesmarcar(){
    $(".marcar").each(
        function() {
            if ($(this).prop("checked")) {
                $(this).prop("checked", false);
            } else {
                $(this).prop("checked", true);
            }
        }
    });
}

The problem is that in if you should test this , not a collection of elements:

function marcardesmarcar() {
    $('.marcar').each(function () {
        if (this.checked) this.checked = false;
        else this.checked = true;
    });
}

While testing $('.marcar').prop("checked") within if , once an element has been changed this if will give true . I assume you want to test the element that is being traversed / iterated.

Example: link

With pure javascript you can get the element by name and assign the checked value of marcar/desmarcar todos to the others in onclick (), because getElementsByName() returns an array.

<script type="text/javascript">
    function marcarTodos(marcar){
        var itens = document.getElementsByName('cores[]');

        if(marcar){
            document.getElementById('acao').innerHTML = 'Desmarcar Todos';
        }else{
            document.getElementById('acao').innerHTML = 'Marcar Todos';
        }

        var i = 0;
        for(i=0; i<itens.length;i++){
            itens[i].checked = marcar;
        }

    }
</script>
<form>
    <input type="checkbox" name="cores[]" onclick="marcarTodos(this.checked);">
     <span id="acao">Marcar</span> <br>
    <input type="checkbox" name="cores[]" value="azul"> azul <br>
    <input type="checkbox" name="cores[]" value="verde"> verde <br>
    <input type="checkbox" name="cores[]" value="branco"> branco <br>
</form>

$("#MarcarTodos").click(function(){
        if ($(this).prop( "checked")){ 
            marcardesmarcar(true);
        }else{
            marcardesmarcar(false);
        }
    });

    function marcardesmarcar(bool){
      $('.marcar').each(
            function(){
               $(this).prop("checked", bool);            
             }
        );
    }

I created the same script in a simpler way:

marcarTodosCheckBoxes: function (seletorCheckBoxes) {
        $(this).prop('checked', !$(this).prop('checked'));
        $(seletorCheckBoxes).prop("checked", $(this).prop("checked"));
    }

Good evening!

I am building a Jquery event library to be used in any project, and I was able to create this same script in this way:

$(document).ready(function(){

   $("#ckAll").click(function()  {  // minha chk que marcará as outras

if ($("#ckAll").prop("checked"))   // se ela estiver marcada... 

$(".chk").prop("checked", true);  // as que estiverem nessa classe ".chk" tambem serão marcadas
     else $(".chk").prop("checked", false);   // se não, elas tambem serão desmarcadas

   });
}); 

works perfectly, and I think it's simple and objective! improved on the basis of the above examples ...