Executing a JavaScript function with no event

Question

Executing a JavaScript function with no event

This particular code snippet is taken from a.jsp:

    <script type="text/javascript" >
    function checkDates(date1, date2)
    {
     var x = date1.split('/')
     var y = date2.split('/')
     var firstDate = new Date(x[2],x[0],x[1])
     var secondDate = new Date(y[2],y[0],y[1])
     var difference = (secondDate - firstDate )
     var daysDifference= difference / (1000 * 60 * 60 * 24);
    }
    </script>

    <% String initialDate="2013/07/12";
       String endDate="2013/07/14";%>

   <script>
    var result=checkDates('$initialDate','$endDate');
   </script>

   <body>
   <% String scriptCode="<script>document.writeln(result)</script>";
      out.println("Output value="+scriptCode); %>
   </body>

The objective here is to extract the number of days (as 'daysDifference') between two given dates ('initialDate' and 'endDate') as an output. However, instead of getting the desired calculation, the current output appears as "Output value=NaN". Can anyone assist in identifying the issue with this coding? Appreciate any help.

java javascript jsp

Answer 1

Answer №1

This particular question proved to be quite challenging to provide a solution for. It seems that the task at hand involves passing variables from a scriptlet to JavaScript using EL. In order to achieve this, it is recommended to:

Declare the variable in the scriptlet as either a pageContext attribute or a request attribute, following the instructions provided here: How to evaluate a scriptlet variable in EL?
Utilize JSTL <c:out> to transfer the variable from EL to your JavaScript function.
In line with GauravSharma's answer suggestion, include a return p; statement at the conclusion of your JavaScript function.

The revised code snippet should resemble the example below (tested on Tomcat 7 and displaying the result "2" in the browser):

<script type="text/javascript">
    function chk(d, e) {
        var x = d.split('/');
        var y = e.split('/');
        var a = new Date(x[0], x[1] - 1, x[2]);
        var b = new Date(y[0], y[1] - 1, y[2]);
        var c = (b - a);
        var p = c / (1000 * 60 * 60 * 24);
        return p;
    }
</script>
<%
    String b = "2013/07/12";
    String c = "2013/07/14";
    pageContext.setAttribute("b", b);
    pageContext.setAttribute("c", c);
%>

<script>
    var myVar = chk('<c:out value="${b}" />', '<c:out value="${c}" />');
</script>

<body>
    <%
        String st = "<script>document.writeln(myVar)</script>";
        out.println("value=" + st);
    %>
</body>

As mentioned in the comment left on your initial question, this scenario serves as a learning exercise for practicing the integration of scriptlets, EL, JSTL, and JavaScript. It is crucial to emphasize that this type of code is not suitable for deployment in a live production environment under any circumstances. The usage of scriptlets has been discouraged for an extended period. For further details, please refer to: How to avoid Java code in JSP files?. Additionally, it would be beneficial to discuss this with your instructor, professor, or tutor responsible for instructing you on Java web development practices.

Answer 2

This particular question proved to be quite challenging to provide a solution for. It seems that the task at hand involves passing variables from a scriptlet to JavaScript using EL. In order to achieve this, it is recommended to:

Declare the variable in the scriptlet as either a pageContext attribute or a request attribute, following the instructions provided here: How to evaluate a scriptlet variable in EL?
Utilize JSTL <c:out> to transfer the variable from EL to your JavaScript function.
In line with GauravSharma's answer suggestion, include a return p; statement at the conclusion of your JavaScript function.

The revised code snippet should resemble the example below (tested on Tomcat 7 and displaying the result "2" in the browser):

<script type="text/javascript">
    function chk(d, e) {
        var x = d.split('/');
        var y = e.split('/');
        var a = new Date(x[0], x[1] - 1, x[2]);
        var b = new Date(y[0], y[1] - 1, y[2]);
        var c = (b - a);
        var p = c / (1000 * 60 * 60 * 24);
        return p;
    }
</script>
<%
    String b = "2013/07/12";
    String c = "2013/07/14";
    pageContext.setAttribute("b", b);
    pageContext.setAttribute("c", c);
%>

<script>
    var myVar = chk('<c:out value="${b}" />', '<c:out value="${c}" />');
</script>

<body>
    <%
        String st = "<script>document.writeln(myVar)</script>";
        out.println("value=" + st);
    %>
</body>

As mentioned in the comment left on your initial question, this scenario serves as a learning exercise for practicing the integration of scriptlets, EL, JSTL, and JavaScript. It is crucial to emphasize that this type of code is not suitable for deployment in a live production environment under any circumstances. The usage of scriptlets has been discouraged for an extended period. For further details, please refer to: How to avoid Java code in JSP files?. Additionally, it would be beneficial to discuss this with your instructor, professor, or tutor responsible for instructing you on Java web development practices.

Answer 3

Answer №2

Make sure to include return p; at the end of your function.
It is important to return a value from your function in order to avoid displaying undefined.

function calculateDaysDifference(startDate, endDate)
{

 var x = startDate.split('/')
 var y = endDate.split('/')
 var a = new Date(x[2],x[0],x[1])
 var b = new Date(y[2],y[0],y[1])
 var c = ( b - a )
 var p= c / (1000 * 60 * 60 * 24);
 return p;
}

Answer 4

Make sure to include return p; at the end of your function.
It is important to return a value from your function in order to avoid displaying undefined.

function calculateDaysDifference(startDate, endDate)
{

 var x = startDate.split('/')
 var y = endDate.split('/')
 var a = new Date(x[2],x[0],x[1])
 var b = new Date(y[2],y[0],y[1])
 var c = ( b - a )
 var p= c / (1000 * 60 * 60 * 24);
 return p;
}

Answer 5

Answer №3

Just use the following code snippet:

var myVariable = check('$b', '$c');

Make sure to call this on document ready.

The reason for this is because JSP has just injected the script into the document, but it has not been executed yet.

Answer 6

Just use the following code snippet:

var myVariable = check('$b', '$c');

Make sure to call this on document ready.

The reason for this is because JSP has just injected the script into the document, but it has not been executed yet.

Executing a JavaScript function with no event

Answer №1

Answer №2

Answer №3

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