未捕获的TypeError：无法读取未定义的属性'prop'

I have 6 input checkboxes and if checkboxes are checked more than 3 the last one gets unchecked. For better understanding refer my previous question. Which is solved.

我有6个输入复选框,如果选中复选框超过3,则最后一个复选框未选中。为了更好地理解,请参阅我之前的问哪个问题解决了。

Now, I have another problem, Now 3 checkboxes are checked already by Math.random. On click of any unchecked checkbox. I'm getting error in console.

现在,我有另一个问题,Math.random现在已经检查了3个复选框。单击任何未选中的复选框。我在控制台中遇到错误。

Uncaught TypeError: Cannot read property 'prop' of undefined

未捕获的TypeError:无法读取未定义的属性'prop'

Fiddle Demo

code below:

var random_checked = $("input[type=checkbox]").get().sort(function(){ 
    return Math.round(Math.random())-0.6; //so we get the right +/- combo
}).slice(0,3);
$(random_checked).prop('checked', true);



var checked = [];
$('input[type=checkbox]').change(function(e) {
    var num_checked = $("input[type=checkbox]:checked").length;
    if (num_checked > 3) {
        checked[checked.length - 1].prop('checked', false);
        checked.pop();
    }
    if($.inArray($(this), checked) < 0){
        checked.push($(this));
    }
});

3 个解决方案

#1

You can try the below code

您可以尝试以下代码

var checked = $('input[type=checkbox]:checked').map(function(){
 return $(this);
}).get(); // First change
$('input[type=checkbox]').change(function(e) {
    var num_checked = $("input[type=checkbox]:checked").length;
    if (num_checked > 3) {
         $(checked.pop()).prop('checked', false);// Second change
    }
    if($.inArray($(this), checked) < 0){
        checked.push($(this));
    }
});

DEMO FIDDLE

Changes Made

► Stored the currently checked elements to an array using

►使用将当前选中的元素存储到数组中

var checked = $('input[type=checkbox]:checked').map(function(){
 return $(this);
}).get();

► $(checked.pop()) is used to select the last inserted element.

►$(checked.pop())用于选择最后插入的元素。

Why your code was not working?

为什么你的代码不起作用?

As per you code var checked = []; will be empty at the initial stage. So checked[checked.length - 1] will become undefined.

根据你的代码var checked = [];在初始阶段将是空的。所以检查[checked.length - 1]将变为未定义。

#2

You should push initial items in checked list.

您应该在已检查列表中推送初始项目。

$(random_checked).each(function(){
    console.log($(this));
    checked.push($(this));
});

https://jsfiddle.net/usx8Lkc5/18/

#3

This one works, just simply adding lastChecked = random_checked[2]; so that your lastChecked is defined.

这个工作,只需添加lastChecked = random_checked [2];这样就定义了你的lastChecked。

var random_checked = $("input[type=checkbox]").get().sort(function(){ 
 var test = Math.round(Math.random())-0.6;
 return test; //so we get the right +/- combo
}).slice(0,3);

$(random_checked).prop('checked', true);
    lastChecked = random_checked[2];
var $checks = $('input:checkbox').click(function(e) {
    var numChecked = $checks.filter(':checked').length;
    if (numChecked > 2) {
        alert("sorry, you have already selected 3 checkboxes!");
        lastChecked.checked = false;
    }
    lastChecked = this;
});

#1