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问题:

I want to have jQuery show div id='business' only if 'business use' is selected in the dropdown box.

This is my code:

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js">
</script>
<script>
$('#purpose').on('change', function() {
  if ( this.value == '1');
  {
    $("#business").show();
  }
  else
  {
    $("#business").hide();
  }
});
});
</script>
<body>
<select id='purpose'>
<option value="0">Personal use</option>
<option value="1">Business use</option>
<option value="2">Passing on to a client</option>
</select>
<div style='display:none;' id='business'>Business Name<br/>&nbsp;
<br/>&nbsp;
    <input type='text' class='text' name='business' value size='20' />
    <br/>
</div>
</body>

and the JSFiddle: http://jsfiddle.net/2kGzZ/1/

回答1:

Wrap the code within $(document).ready(function(){...........}); handler , also remove the ; after if

$(document).ready(function(){
    $('#purpose').on('change', function() {
      if ( this.value == '1')
      //.....................^.......
      {
        $("#business").show();
      }
      else
      {
        $("#business").hide();
      }
    });
});

Fiddle Demo

回答2:

You need to either put your code at the end of the page or wrap it in a document ready call, otherwise you're trying to execute code on elements that don't yet exist. Also, you can reduce your code to:

$('#purpose').on('change', function () {
    $("#business").css('display', (this.value == '1') ? 'block' : 'none');
});

jsFiddle example

回答3:

The core problem is the js errors:

$('#purpose').on('change', function () {
    // if (this.value == '1'); { No semicolon and I used === instead of ==
    if (this.value === '1'){
        $("#business").show();
    } else {
        $("#business").hide();
    }
});
// }); remove

http://jsfiddle.net/Bushwazi/2kGzZ/3/

I had to clean up the html & js...I couldn't help myself.

HTML:

<select id='purpose'>
    <option value="0">Personal use</option>
    <option value="1">Business use</option>
    <option value="2">Passing on to a client</option>
</select>
<form id="business">
    <label for="business">Business Name</label>
    <input type='text' class='text' name='business' value size='20' />
</form>

CSS:

#business {
  display:none;
}

JS:

$('#purpose').on('change', function () {
    if(this.value === "1"){
        $("#business").show();
    } else {
        $("#business").hide();
    }
});

回答4:

you have error in your code unexpected token.use:

  $('#purpose').on('change', function () {
   if (this.value == '1') {
    $("#business").show();
    } else {
    $("#business").hide();
   }

   });

Demo

Update: You can narrow down the code using .toggle()

 $('#purpose').on('change', function () {
   $("#business").toggle(this.value == '1');
 });

回答5:

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js">
</script>
<script>
$(document).ready(function(){
    $('#purpose').on('change', function() {
      if ( this.value == '1')
      //.....................^.......
      {
           $("#business_new").hide();
        $("#business").show();
      }
      else  if ( this.value == '2')
      {
          $("#business").hide();
        $("#business_new").show();
      }
       else  
      {
        $("#business").hide();
      }
    });
});
</script>
<body>
<select id='purpose'>
<option value="0">Personal use</option>
<option value="1">Business use</option>
<option value="2">Passing on to a client</option>
</select>
<div style='display:none;' id='business'>Business Name<br/>&nbsp;
<br/>&nbsp;
    <input type='text' class='text' name='business' value size='20' />
    <input type='text' class='text' name='business' value size='20' />
    <br/>
</div>
<div style='display:none;' id='business_new'>Business Name<br/>&nbsp;
<br/>&nbsp;
    <input type='text' class='text' name='business' value="1254" size='20' />
    <input type='text' class='text' name='business' value size='20' />
    <br/>
</div>
</body>

回答6:

try this which is working for me in my test demo

<script>
$(document).ready(function(){
$('#dropdown').change(function() 
{ 
//  var selectedValue = parseInt(jQuery(this).val());
var text = $('#dropdown').val();
//alert("text");
    //Depend on Value i.e. 0 or 1 respective function gets called. 
    switch(text){
        case 'Reporting':
          // alert("hello1");
   $("#td1").hide();
            break;
        case 'Buyer':
      //alert("hello");
     $("#td1").show();   
            break;
        //etc... 
        default:
            alert("catch default");
            break;
    }
});
});

</script>