JQuery limitar caracteres - keyup - enter

$("#img_title").keyup(function(){
        var max = 13;
        if($("#img_title").val().length>max){
            $("#img_title").val($("#img_title").val().substr(0, max));
            alert("Number of caracters max allowed is: "+ max);
        }
    });

$('#input_text').keyup(function(e) {
    //alert(e.keyCode);
    if(e.keyCode == 13) {
        alert('Enter key was pressed.');
    }
});