if statement - Javascript: comparing two values always not equal - Stack Overflow

admin管理员组

文章数量:1379395

I'm trying to do something but im struggling with a stupid bug, hope you can help me.

As you can see in my code I have on server some check box and I attached to it a JavaScript function. This function gets two values (current value and original value). My problem is when this function triggers on the if it always get to the first clause and never reach the else clause and it doesn't make any sense.

When I used few alerts in my code this is what happens:

case 1: alert #1 original: false current: true alert #2 true

case 2: alert #1 original: false current: false alert #2 true

As you can see, no matter what I get true on the 2nd alert.

Hope I managed to explain my problem.

<asp:CheckBox id="chkIsCustomQuantity" originalvalue="false" runat="server" onclick="checkChange(this.checked, this.attributes['originalvalue'].value" />

<script type="text/javascript" language="javascript">
    function checkChange(value, originalValue) {

        //i added this for debugging purpose
        alert('original: ' + originalValue + ' ' + 'current: ' + value);
        alert(value != originalValue);

        if (value != originalValue) {
             // always happens
        }
        else {
              // never happens
        }
    }

</script>

I'm trying to do something but im struggling with a stupid bug, hope you can help me.

As you can see in my code I have on server some check box and I attached to it a JavaScript function. This function gets two values (current value and original value). My problem is when this function triggers on the if it always get to the first clause and never reach the else clause and it doesn't make any sense.

When I used few alerts in my code this is what happens:

case 1: alert #1 original: false current: true alert #2 true

case 2: alert #1 original: false current: false alert #2 true

As you can see, no matter what I get true on the 2nd alert.

Hope I managed to explain my problem.

<asp:CheckBox id="chkIsCustomQuantity" originalvalue="false" runat="server" onclick="checkChange(this.checked, this.attributes['originalvalue'].value" />

<script type="text/javascript" language="javascript">
    function checkChange(value, originalValue) {

        //i added this for debugging purpose
        alert('original: ' + originalValue + ' ' + 'current: ' + value);
        alert(value != originalValue);

        if (value != originalValue) {
             // always happens
        }
        else {
              // never happens
        }
    }

</script>

• javascript
• if-statement

Share Improve this question Follow edited Feb 19, 2012 at 21:49 user1106925 asked Feb 19, 2012 at 21:31 PopokokoPopokoko 6,5431616 gold badges5050 silver badges5858 bronze badges 2

• 1 Use console.log and/or your debugger to inspect variable values. Trust me, you will never want to go back to alert() after that. – hugomg Commented Feb 19, 2012 at 21:37
• Unless you're a 13-year-old girl, "u" is not a word. Please use proper English. – user1106925 Commented Feb 19, 2012 at 21:37

Add a ment  | 

1 Answer 1

Sorted by: Reset to default 6

originalValue is always a string. value is a boolean. So, they're never equal, but when you print them out they appear identical (since they're both converted to the same string value at that point).

You can fix this in a variety of ways. One simple way is to convert both to strings first:

if (String(value) != String(originalValue))

本文标签： if statementJavascript comparing two values always not equalStack Overflow