javascript - 复选框数量可变限制

Question

我想限制复选框的数量，但不使用固定数量(即 2)，但我想预先选择此限制。

我可以限制在 fix way (working example)

 <p>Select your favorite countries below:</p>

<form id="world" name="world">
Select the limit<select id="limit" onchange="this.form.submit()"><option value="1">1</option><option value="2">2</option></select><br/>
 <input type="checkbox" name="countries" /> USA<br />
 <input type="checkbox" name="countries" /> Canada<br />
 <input type="checkbox" name="countries" /> Japan<br />
 <input type="checkbox" name="countries" /> China<br />
<input type="checkbox" name="countries" /> France<br />
</form>


function checkboxlimit(checkgroup, limit){
var checkgroup=checkgroup
var limit=limit
for (var i=0; i<checkgroup.length; i++){
    checkgroup[i].onclick=function(){
    var checkedcount=0
    for (var i=0; i<checkgroup.length; i++)
        checkedcount+=(checkgroup[i].checked)? 1 : 0
    if (checkedcount>limit){
        alert("You can only select a maximum of "+limit+" checkboxes")
        this.checked=false
        }
    }
}
}


checkboxlimit(document.forms.world.countries, 2)

但我无法更改此 variable way (not working) 中的限制

<p>Select your favorite countries below:</p>

<form id="world" name="world">
Select the limit<select id="limit" onchange="this.form.submit()"><option value="1">1</option><option value="2">2</option></select><br/>
<input type="checkbox" name="countries" /> USA<br />
<input type="checkbox" name="countries" /> Canada<br />
<input type="checkbox" name="countries" /> Japan<br />
<input type="checkbox" name="countries" /> China<br />
<input type="checkbox" name="countries" /> France<br />
</form>



function checkboxlimit(checkgroup, limit){
var checkgroup=checkgroup
var limit=limit
for (var i=0; i<checkgroup.length; i++){
    checkgroup[i].onclick=function(){
    var checkedcount=0
    for (var i=0; i<checkgroup.length; i++)
        checkedcount+=(checkgroup[i].checked)? 1 : 0
    if (checkedcount>limit){
        alert("You can only select a maximum of "+limit+" checkboxes")
        this.checked=false
        }
    }
}
}

var e = document.getElementById("limit");
var limit = e.options[e.selectedIndex].value;
checkboxlimit(document.forms.world.countries, limit)

Answer 1

这是一个可能的解决方案:https://jsfiddle.net/g6cyegnt/1/

您所要做的就是不要在限制控制的更改事件上提交表单。单独处理change事件，如代码/fiddler所示。

<p>Select your favorite countries below:</p>

<form id="world" name="world">
    Select the limit<select id="limit"><option value="1">1</option><option value="2">2</option></select><br/>
<input type="checkbox" name="countries" /> USA<br />
<input type="checkbox" name="countries" /> Canada<br />
<input type="checkbox" name="countries" /> Japan<br />
<input type="checkbox" name="countries" /> China<br />
<input type="checkbox" name="countries" /> France<br />
</form>

function checkboxlimit(checkgroup, limit){
    var checkgroup=checkgroup
    var limit=limit
    for (var i=0; i<checkgroup.length; i++){
        checkgroup[i].onclick=function(){
        var checkedcount=0
        for (var i=0; i<checkgroup.length; i++)
            checkedcount+=(checkgroup[i].checked)? 1 : 0
        if (checkedcount>limit){
            alert("You can only select a maximum of "+limit+" checkboxes")
            this.checked=false
            }
        }
    }
}

$('input[name="countries"]').on('change', function(){
var limit = $('#limit').find(':selected').val();
checkboxlimit(document.forms.world.countries, limit)
});