HTML SELECT - Trigger JavaScript ONCHANGE event ev

问题:

I have the following markup:

<select onchange="jsFunction()">
    <option value="1">1</option>
    <option value="2">2</option>
    <option value="3">3</option>
</select>

When a user pulls down the combobox and selects the same option that was previously selected (or doesn't change the selection at all), JavaScript doesn't regard it as an onchange event. So, the jsFunction() is not called. But I want the jsFunction() called even in this case. How can I achieve this?

回答1:

I'd do it like this:

<select onchange="jsFunction()">
  <option value="" disabled selected style="display:none;">Label</option>
  <option value="1">1</option>
  <option value="2">2</option>
  <option value="3">3</option>
</select>

If you want you could have the same label as the first option, which in this case is 1. Even better: put a label in there for the choices in the box.

回答2:

You have to add empty option to solve it,

I also can give you one more solution but its up to you that is fine for you or not Because User select default option after selecting other options than jsFunction will be called twice.

<select onChange="jsFunction()" id="selectOpt">
    <option value="1" onclick="jsFunction()">1</option>
    <option value="2">2</option>
    <option value="3">3</option>
</select>

function jsFunction(){
  var myselect = document.getElementById("selectOpt");
  alert(myselect.options[myselect.selectedIndex].value);
}

回答3:

This works:

<select name="type" onmousedown="this.value='';" onchange="alert('Changed.');">
  <option value='1'>One</option>
  <option value='2'>Two</option>
  <option value='3'>Three</option>
  <option value='4'>Four</option>
  <option value='5'>Five</option>
  <option value='6'>Six</option>
  <option value='7'>Seven</option>
  <option value='8'>Eight</option>
  <option value='9'>Nine</option>
  <option value='10'>Ten</option> 
</select>

回答4:

use the "onmouseup" property with each option element. it's verbose, but should work. also, depending on what your function is actually doing, you could arrange things a little differently, assuming the number is important in the handler:

<select>
<option onmouseup="handler()" value="1">1</option>  //get selected element in handler
<option onmouseup="handler(2)" value="2">2</option>  //explicitly send the value as argument
<option onmouseup="handler(this.value)" value="3">3</option> //same as above, but using the element's value property and allowing for dynamic option value. you could also send "this.innerHTML" or "this.textContent" to the handler, making option value unnecessary
</select>

回答5:

JavaScript code:

• on mousedown event: set selectedIndex property value to -1
• on change event: handle event

The only drawback is that when the user clicks on the dropdown list, the currently selected item does not appear selected

回答6:

Just set the selectIndex of the associated <select> tag to -1 as the last step of your processing event.

mySelect = document.getElementById("idlist");
mySelect.selectedIndex = -1; 

It works every time, removing the highlight and allowing you to select the same (or different) element again .

回答7:

It's not firing because the value hasn't "changed". It's the same value. Unfortunately, you can't achieve the desired behaviour using the change event.

You can handle the blur event and do whatever processing you need when the user leaves the select box. That way you can run the code you need even if the user selects the same value.

回答8:

Try this. Just add an empty option. This will solve your problem.

<select onchange="jsFunction()">
    <option></option>
    <option value="1">1</option>
    <option value="2">2</option>
    <option value="3">3</option>
</select>​