javascript - 为什么长度显示为未定义？

Question

<div class="aa">
  <input type='radio' id="1" name='choices' value='1'/>
  <input type='radio' id ="2" name='choices' value='2'/>

  <input type='radio' id="3" name='choices1' value='3'/>
  <input type='radio' id="4" name='choices1' value='4'/>
</div>

jQuery

$(".aa :radio").change(function() {

  var names = {};
  $('.aa :radio').each(function() { // find unique names
    names[$(this).attr('name')] = true;
  });
  var count = 0;
  $.each(names, function() { // then count them
    count++;
  });
  alert ("count " + count +  " length " + names.length); //names length comes up as undefined why?
}).change();

Answer 1

因为names是一个对象而不是数组。在您的示例中，计数将是对象名称中键的长度。

获取键的长度:

var count = 0;
for(var i in names) {
  count++;
} 
count; // length

或现代浏览器Object.keys(names).length