How do I debug JavaScript

Hi Experts,

Can anyone tell me how to properly debug JavaScript, as I feel browsers messages are often misleading.

For example, I keep getting
SyntaxError: missing ; before statement login:68


My source code is
 <!DOCTYPE html>
<html lang="en">

 <head>
	<meta charset="utf-8">
        <title>RS @ APD</title>
	<link rel="stylesheet" href="https://localhost/CSS_Reservations/styles/main.css">
        <link rel="stylesheet" href="https://localhost/CSS_Reservations/styles/buttons.css">
        <link rel="stylesheet" href="https://localhost/CSS_Reservations/styles/forms.css">
        <link rel="stylesheet" href="https://localhost/CSS_Reservations/styles/scroll-table.css">
	
</head>

    <body>

        <h1>RS @ APD</h1><br>
        <h2>Change Login Password</h2>
        
        <!--Content Start-->

    <!--content-->
    
    <!--Place where appropriate-->
    
 
    
            <!--Content Start-->
        <form name="frm" id="frm" autocomplete="off" method="post" action="?action=PW_Change"
              onSubmit="return checkRequired();">
            <fieldset>
                
            <input type="hidden" name="hidUserID"  id="hidUserID" value="1">
            
            <label for="txtUser" class="required" >User:</label>
            <input type="text" name="txtUser" id="txtUser" value="reservations"
                   readonly="readonly"><br><br>
            
            <label for="txtPWold" class="required">Current Password:</label>
            <input type="password" name="txtPWold" id="txtPWold" maxlength="255" class="required"><br><br>
                        
            <label for="txtPWnew1" class="required">New Password:</label>
            <input type="password" name="txtPWnew1" id="txtPWnew1" maxlength="255" class="required"><br><br>
            
            <label for="txtPWnew2" class="required">Retype Password:</label>
            <input type="password" name="txtPWnew2" id="txtPWnew2" maxlength="255" class="required"><br><br>
            
            <label>&nbsp;</label>
            <input type="submit" id="btnSave" value="Save Changes" class="button">
            <input type="button" id="btnCancel" value="Cancel Changes" onClick="cancelChanges();" class="button"><br>
            </fieldset>        
        </form> 
            
<script type="text/javascript">

    function cancelChanges(){
        if (confirm("Are you sure you want to cancel these changes?")) {
        self.location = "index.php?action=pw_cancel";
        }
    }
    
    function checkRequired(){
        var pwOld = frm.txtPWold.value();
        var pw1 = frm.txtPWnew1.value();
        var pw2 = frm.txtPWnew2.value();
    
        if (pwOld == ''){
            alert 'Must specify old password.';
            return false;
        }
        
        if (pw1.length < 5){
            alert 'The new password must be 5 characters or more.';
            return false;
        }
        
        if (pw1 != pw2){
            alert 'New Password and Retype Password must match.';
            return false;
        }
        
        //all pass
        return true;
    }
  
</script>

        <!--Content Finish-->

    </body>
 
 </html>

Open in new window


Thanks
APD TorontoAsked:
Who is Participating?
 
Dave BaldwinFixer of ProblemsCommented:
Sorry, the browsers are the final word on their version of javascript.  IE, Firefox, and Chrome all have slightly different versions of javascript.  And when you run into that slight difference, you will see an error on one and not the others.  IE in my experience has been the pickiest.
0
 
Jeff DarlingDeveloper AnalystCommented:
have you ever used jsfiddle?

jsfiddle example using your code

One nice thing is the lint feature.  It helps find code errors.
0
 
APD TorontoAuthor Commented:
But, how do I pinpoint, for example the above error?  Whats wrong with it?
0
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Dave BaldwinFixer of ProblemsCommented:
'alert' text requires () around them like this:
 <!DOCTYPE html>
<html lang="en">

 <head>
	<meta charset="utf-8">
        <title>RS @ APD</title>
	<link rel="stylesheet" href="https://localhost/CSS_Reservations/styles/main.css">
        <link rel="stylesheet" href="https://localhost/CSS_Reservations/styles/buttons.css">
        <link rel="stylesheet" href="https://localhost/CSS_Reservations/styles/forms.css">
        <link rel="stylesheet" href="https://localhost/CSS_Reservations/styles/scroll-table.css">
	
</head>

    <body>

        <h1>RS @ APD</h1><br>
        <h2>Change Login Password</h2>
        
        <!--Content Start-->

    <!--content-->
    
    <!--Place where appropriate-->
    
 
    
            <!--Content Start-->
        <form name="frm" id="frm" autocomplete="off" method="post" action="?action=PW_Change"
              onSubmit="return checkRequired();">
            <fieldset>
                
            <input type="hidden" name="hidUserID"  id="hidUserID" value="1">
            
            <label for="txtUser" class="required" >User:</label>
            <input type="text" name="txtUser" id="txtUser" value="reservations"
                   readonly="readonly"><br><br>
            
            <label for="txtPWold" class="required">Current Password:</label>
            <input type="password" name="txtPWold" id="txtPWold" maxlength="255" class="required"><br><br>
                        
            <label for="txtPWnew1" class="required">New Password:</label>
            <input type="password" name="txtPWnew1" id="txtPWnew1" maxlength="255" class="required"><br><br>
            
            <label for="txtPWnew2" class="required">Retype Password:</label>
            <input type="password" name="txtPWnew2" id="txtPWnew2" maxlength="255" class="required"><br><br>
            
            <label>&nbsp;</label>
            <input type="submit" id="btnSave" value="Save Changes" class="button">
            <input type="button" id="btnCancel" value="Cancel Changes" onClick="cancelChanges();" class="button"><br>
            </fieldset>        
        </form> 
            
<script type="text/javascript">

    function cancelChanges(){
        if (confirm("Are you sure you want to cancel these changes?")) {
        self.location = "index.php?action=pw_cancel";
        }
    	}
    
    function checkRequired(){
        var pwOld = frm.txtPWold.value();
        var pw1 = frm.txtPWnew1.value();
        var pw2 = frm.txtPWnew2.value();
    
        if (pwOld == ''){
            alert ('Must specify old password.');
            return false;
        }
        
        if (pw1.length < 5){
            alert ('The new password must be 5 characters or more.');
            return false;
        }
        
        if (pw1 != pw2){
            alert ('New Password and Retype Password must match.');
            return false;
        }
        
        //all pass
        return true;
    }
  
</script>

        <!--Content Finish-->

    </body>
 
 </html>

Open in new window

0
 
APD TorontoAuthor Commented:
How does jsfiddle help?

When I click Save - I get "Forbidden", and Cancel does nothing.

I can't see that it outlines any errors?
0
 
APD TorontoAuthor Commented:
That fixed cancel, but Save still submits even if fields are blank
0
 
Jeff DarlingDeveloper AnalystCommented:
sorry, I forgot to mention that I fixed a couple of the errors.

specifically the alert statements.  


https://jsfiddle.net/jeffld/9xugf01w/3/

click the jshint button to see the lines that have a problem.
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OriNetworksCommented:
For basic syntax checking, You could use an online syntax validator http://esprima.org/demo/validate.html
 Although most IDE such as visual studio will highlight errors for you. As for runtime errors you can use browser tools such as internet explorer F12 developer tools. The console tab will show errors as they occur or you can search for a tutorial to set breakpoints, view network traffic, inspect values in realtime. Tools also exist for firefox and chrome
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Dave BaldwinFixer of ProblemsCommented:
I don't see any () around the 'alert' texts.  ??  That is what the original error is.
0
 
APD TorontoAuthor Commented:
In JSFiddle I added () in all alerts, and added 3 === on line 12. I also did the same changes in my local environment, but still "Save Changes" does not work. For example it submits when the current password is empty, but in this case JS should return False and cancel out the Submit as per line 14. Why is this not happening?

As well, why 3 ===, and my IDE (NetBeans) suggested !== on line 22, but why? Even with these changes, Save does not cancel submission.

Please advise
0
 
APD TorontoAuthor Commented:
Had to remove () after .value
0
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