Javascript comparing boolean value to True

Question

I am trying to compare a database (SQL) value (which is being returned correctly) to the boolean value 'true'. If the database bit value is = true then I want a div element to become visible, else stay hidden.

<script language="javascript">
    window.onload= function show_CTL() {
        if(<%=_CurrentUser.IsCTL%> == true){
            document.getElementById('CTL').style.visibility = "visible";
        } else{
            document.getElementById('CTL').style.visibility = "hidden";
        }
    }    
</script>

However I am getting the error, Javascript: 'True' is undefined.

I have tried many combinations of <%=_CurrentUser.IsCTL%> == 'true' or "true" or true or "True" or 'true' and even the === ... but all give me the same error message.

Any insights on how to resolve this issue will be greatly appreciated.

I have such comparisons successfully before with integer values such as:-

 window.onload= function show() {
    if(<%=_CurrentUser.RoleKey%> == 1 || <%=_CurrentUser.RoleKey%> == 2)
            document.getElementById('enr').style.visibility = "visible";
    else
            document.getElementById('enr').style.visibility = "hidden";
 }

What language is `<%=_CurrentUser.IsCTL%>` and what does it output? — j08691, Apr 16 '14 at 16:59
it outputs true or false (boolean) values. appropriately for currently logged in user. — Philo, Apr 16 '14 at 17:00
Try `if("<%=_CurrentUser.IsCTL%>" == "True")` or `if(<%=_CurrentUser.IsCTL.ToString().ToLower()%> == true)` — Musa, Apr 16 '14 at 17:02
What dose the code look like when it's sent to the browser? You're probably getting `True == true`, hence your error. `True` is an undefined variable in JS, `true` is a boolean value... — Marc B, Apr 16 '14 at 17:03
The lhs of your equal is inserting the four letters `True`. Try enclosing them in quotes to make it a string and comparing them to the string "True". — thebjorn, Apr 16 '14 at 17:03
a tip: always enclose the jsp expr in quotes as "<%=_CurrentUser.IsCTL%>", since if it empty string then it will be if(==true) which is a wrong syntax and might fail in this scenario. — vivek_nk, Apr 16 '14 at 17:03

score 5 · Accepted Answer · edited Sep 01 '16 at 19:22

5

Do this:

if("<%=_CurrentUser.IsCTL%>" === "True")

<%=_CurrentUser.IsCTL%> is returning True. So wrap it with string and compare them instead. Notice the '===' instead of '=='.

edited Sep 01 '16 at 19:22

Community

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1

answered Apr 16 '14 at 16:59

Amit Joki

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Hi Amit, as mentioned in my statement, that doesn't work. I have tried some possible combinations and I have mentioned them in my question. – Philo Apr 16 '14 at 17:01
2

@Philo, you didn't see my answer properly. I'm wrapping both with strings – Amit Joki Apr 16 '14 at 17:02
Why you use single and double quotes? Why not both single or both double? – martijnn2008 Apr 16 '14 at 17:03
1

@martijnn2008, it doesn't matter ;) – Amit Joki Apr 16 '14 at 17:04
@martijnn2008 check this one. http://stackoverflow.com/questions/242813/when-to-use-double-or-single-quotes-in-javascript – vivek_nk Apr 16 '14 at 17:05
I though it would not make a difference, but I do expect some consistency, so that is why I asked for a particular reason. – martijnn2008 Apr 16 '14 at 17:08
One more problem :- even the return value is true, the condition for false always gets evaluated... – Philo Apr 16 '14 at 17:17

score 2 · Answer 2 · answered Apr 16 '14 at 17:05

2

In

if(<%=_CurrentUser.IsCTL%> == true)

I think <%=_CurrentUser.IsCTL%> is getting evaluated to True before the code is seen by the browser.
The browser will see this as

if(True == true)

True does not make a lot of sense to the browser, thats why the error. For this true to be treated as a boolean, try one of this:

if(new Boolean('<%=_CurrentUser.IsCTL%>') == true)

or

if(new Boolean('<%=_CurrentUser.IsCTL%>'))

answered Apr 16 '14 at 17:05

Nivas

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That doesn't work the way you think it does... `(new Boolean("False")) ? "TRUE" : "FALSE"` evaluates to... `"TRUE"` – thebjorn Apr 16 '14 at 17:12
@thebjorn you are right. Confused Java's behaviour with Javascript's behaviour. – Nivas Apr 16 '14 at 19:50

score 2 · Answer 3 · answered Apr 16 '14 at 17:05

This has gotten me before as well. ASP.NET will return True for a boolean which is true. You have to make it a string and then compare it to the string version == "True" in order to get a proper conditional statement.

Conversely, you could also just make a variable in javascript

var True = true;

score 0 · Answer 4 · answered Apr 16 '14 at 17:11

0

You need to convert your native boolean value to the string "true" before output. So, assuming ASP.NET MVC, I believe it looks like:

<%=_CurrentUser.IsCTL ? "true" : "false"%>

answered Apr 16 '14 at 17:11

Chuck

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Javascript comparing boolean value to True

4 Answers4