javascript - Disable dropdownlist based on the selected value of another - Stack Overflow

admin管理员组

文章数量:1379561

This may be a stupid question, but I'm still learning so do forgive me if the answer is obvious :)

I have a test page with the following on:

<select name="ddlRoles" ID="ddlRoles" OnChange="DisEnableDDL();">
<option value="-1">Fresh Milk</option>
<option value="2">Old Cheese</option>
<option value="3">Hot Bread</option>
</select>
<select name="ddlCust" ID="ddlCust">
<option value="-1">rawr</option>
<option value="2">root</option>
<option value="3">honk</option>
</select>

If the user selects anything with a value that's not 3 from ddl Roles, it should disable ddlCust. Here's my JS function:

function DisEnableDDL()
{
var ddlR = document.getElementById("ddlRoles")
var ddlC = document.getElementById("ddlCust")
if(ddlR.options[ddlR.selectedIndex].value = "3")
 {
    ddlC.disabled = false;
 }
else
 {
    ddlC.selectedIndex = 0;
    ddlC.disabled = true;    
 }
}

Doesn't work. What am I missing? have I failed to set my variables properly? Does this just change the variables ddlR and ddlC without changing the elements on the page itself or something? Following it through in Firebug, it seems to fall into the correct statements, but ddlCust never gets disabled.

Any help would be most appreciated!

This may be a stupid question, but I'm still learning so do forgive me if the answer is obvious :)

I have a test page with the following on:

<select name="ddlRoles" ID="ddlRoles" OnChange="DisEnableDDL();">
<option value="-1">Fresh Milk</option>
<option value="2">Old Cheese</option>
<option value="3">Hot Bread</option>
</select>
<select name="ddlCust" ID="ddlCust">
<option value="-1">rawr</option>
<option value="2">root</option>
<option value="3">honk</option>
</select>

If the user selects anything with a value that's not 3 from ddl Roles, it should disable ddlCust. Here's my JS function:

function DisEnableDDL()
{
var ddlR = document.getElementById("ddlRoles")
var ddlC = document.getElementById("ddlCust")
if(ddlR.options[ddlR.selectedIndex].value = "3")
 {
    ddlC.disabled = false;
 }
else
 {
    ddlC.selectedIndex = 0;
    ddlC.disabled = true;    
 }
}

Doesn't work. What am I missing? have I failed to set my variables properly? Does this just change the variables ddlR and ddlC without changing the elements on the page itself or something? Following it through in Firebug, it seems to fall into the correct statements, but ddlCust never gets disabled.

Any help would be most appreciated!

• javascript

Share Improve this question Follow asked Jun 19, 2009 at 10:31 RYFNRYFN 3,08911 gold badge3131 silver badges4141 bronze badges

Add a ment  | 

2 Answers 2

Sorted by: Reset to default 3

== instead of = in your if:

if(ddlR.options[ddlR.selectedIndex].value == "3")

= is for assignment, whereas == is for parison, in most C-like syntaxes.

You're not paring properly, you need to use '==':

if(ddlR.options[ddlR.selectedIndex].value == "3")

本文标签：