Develop Reference

How to obtain values of variables passed to ejs in a linked javascript file in electron

I am trying to build an electron app. An EJS file has variable values passed to it from the main process. I want to obtain these variables in the javascript file linked to renderer process. I tried the following :
<script>
var details = <%= details %>
</script>
But I recieve an error expression expected.
How can I do this? I am new to electron and nodejs, any help is appreciated. Thanks!

Look at the generated source code.
If the value of details is, when you convert it to a string, anything other than valid JS syntax then this will error.
For example, if details = "Hello, world" then the generated HTML page will look like this:
<script>
var details = Hello, world
</script>
which will treat Hello like a variable name and then error.
You need to encode your data
Since JSON was designed as a subset of JS literal syntax, you can encode it as then and then the client-side JS parser will convert it back to an object / string / whatever it was in the first place.
var details = <%- JSON.stringify(details) %>

Don't think you need to use any decorations since you are already in JS.
Try this:
<script>console.log(details);</script>

How a Session variable set in Server be accessed in External javascript file? [duplicate]

I have a form in JSP. I have to populate it based on the request object (from the servlet). How do I use Java Script for accessing request object attributes or if you can suggest me any other better way to populate form dynamically?

You need to realize that Java/JSP is merely a HTML/CSS/JS code producer. So all you need to do is to just let JSP print the Java variable as if it is a JavaScript variable and that the generated HTML/JS code output is syntactically valid.
Provided that the Java variable is available in the EL scope by ${foo}, here are several examples how to print it:
<script>var foo = '${foo}';</script>
<script>someFunction('${foo}');</script>
<div onclick="someFunction('${foo}')">...</div>
Imagine that the Java variable has the value "bar", then JSP will ultimately generate this HTML which you can verify by rightclick, View Source in the webbrowser:
<script>var foo = 'bar';</script>
<script>someFunction('bar');</script>
<div onclick="someFunction('bar')">...</div>
Do note that those singlequotes are thus mandatory in order to represent a string typed variable in JS. If you have used var foo = ${foo}; instead, then it would print var foo = bar;, which may end up in "bar is undefined" errors in when you attempt to access it further down in JS code (you can see JS errors in JS console of browser's web developer toolset which you can open by pressing F12 in Chrome/FireFox23+/IE9+). Also note that if the variable represents a number or a boolean, which doesn't need to be quoted, then it will just work fine.
If the variable happens to originate from user-controlled input, then keep in mind to take into account XSS attack holes and JS escaping. Near the bottom of our EL wiki page you can find an example how to create a custom EL function which escapes a Java variable for safe usage in JS.
If the variable is a bit more complex, e.g. a Java bean, or a list thereof, or a map, then you can use one of the many available JSON libraries to convert the Java object to a JSON string. Here's an example assuming Gson.
String someObjectAsJson = new Gson().toJson(someObject);
Note that this way you don't need to print it as a quoted string anymore.
<script>var foo = ${someObjectAsJson};</script>
See also:
Our JSP wiki page - see the chapter "JavaScript".
How to escape JavaScript in JSP?
Call Servlet and invoke Java code from JavaScript along with parameters
How to use Servlets and Ajax?

If you're pre-populating the form fields based on parameters in the HTTP request, then why not simply do this on the server side in your JSP... rather than on the client side with JavaScript? In the JSP it would look vaguely like this:
<input type="text" name="myFormField1" value="<%= request.getParameter("value1"); %>"/>
On the client side, JavaScript doesn't really have the concept of a "request object". You pretty much have to parse the query string yourself manually to get at the CGI parameters. I suspect that isn't what you're actually wanting to do.

Passing JSON from JSP to Javascript.
I came here looking for this, #BalusC's answer helped to an extent but didn't solve the problem to the core. After digging deep into <script> tag, I came across this solution.
<script id="jsonData" type="application/json">${jsonFromJava}</script>
and in the JS:
var fetchedJson = JSON.parse(document.getElementById('jsonData').textContent);

In JSP file:
<head>
...
<%# page import="com.common.Constants" %>
...
</head>
<script type="text/javascript">
var constant = "<%=Constants.CONSTANT%>"
</script>
This constant variable will be then available to .js files that are declared after the above code.
Constants.java is a java file containing a static constant named CONSTANT.
The scenario that I had was, I needed one constant from a property file, so instead of constructing a property file for javascript, I did this.

In JSP page :
<c:set var="list_size" value="${list1.size() }"></c:set>
Access this value in Javascipt page using :
var list_size = parseInt($('#list_size').val());
I added javascript page in my project externally.

How to access c:set variable from jsp to javascript not working [duplicate]

I have a form in JSP. I have to populate it based on the request object (from the servlet). How do I use Java Script for accessing request object attributes or if you can suggest me any other better way to populate form dynamically?

You need to realize that Java/JSP is merely a HTML/CSS/JS code producer. So all you need to do is to just let JSP print the Java variable as if it is a JavaScript variable and that the generated HTML/JS code output is syntactically valid.
Provided that the Java variable is available in the EL scope by ${foo}, here are several examples how to print it:
<script>var foo = '${foo}';</script>
<script>someFunction('${foo}');</script>
<div onclick="someFunction('${foo}')">...</div>
Imagine that the Java variable has the value "bar", then JSP will ultimately generate this HTML which you can verify by rightclick, View Source in the webbrowser:
<script>var foo = 'bar';</script>
<script>someFunction('bar');</script>
<div onclick="someFunction('bar')">...</div>
Do note that those singlequotes are thus mandatory in order to represent a string typed variable in JS. If you have used var foo = ${foo}; instead, then it would print var foo = bar;, which may end up in "bar is undefined" errors in when you attempt to access it further down in JS code (you can see JS errors in JS console of browser's web developer toolset which you can open by pressing F12 in Chrome/FireFox23+/IE9+). Also note that if the variable represents a number or a boolean, which doesn't need to be quoted, then it will just work fine.
If the variable happens to originate from user-controlled input, then keep in mind to take into account XSS attack holes and JS escaping. Near the bottom of our EL wiki page you can find an example how to create a custom EL function which escapes a Java variable for safe usage in JS.
If the variable is a bit more complex, e.g. a Java bean, or a list thereof, or a map, then you can use one of the many available JSON libraries to convert the Java object to a JSON string. Here's an example assuming Gson.
String someObjectAsJson = new Gson().toJson(someObject);
Note that this way you don't need to print it as a quoted string anymore.
<script>var foo = ${someObjectAsJson};</script>
See also:
Our JSP wiki page - see the chapter "JavaScript".
How to escape JavaScript in JSP?
Call Servlet and invoke Java code from JavaScript along with parameters
How to use Servlets and Ajax?

If you're pre-populating the form fields based on parameters in the HTTP request, then why not simply do this on the server side in your JSP... rather than on the client side with JavaScript? In the JSP it would look vaguely like this:
<input type="text" name="myFormField1" value="<%= request.getParameter("value1"); %>"/>
On the client side, JavaScript doesn't really have the concept of a "request object". You pretty much have to parse the query string yourself manually to get at the CGI parameters. I suspect that isn't what you're actually wanting to do.

Passing JSON from JSP to Javascript.
I came here looking for this, #BalusC's answer helped to an extent but didn't solve the problem to the core. After digging deep into <script> tag, I came across this solution.
<script id="jsonData" type="application/json">${jsonFromJava}</script>
and in the JS:
var fetchedJson = JSON.parse(document.getElementById('jsonData').textContent);

In JSP file:
<head>
...
<%# page import="com.common.Constants" %>
...
</head>
<script type="text/javascript">
var constant = "<%=Constants.CONSTANT%>"
</script>
This constant variable will be then available to .js files that are declared after the above code.
Constants.java is a java file containing a static constant named CONSTANT.
The scenario that I had was, I needed one constant from a property file, so instead of constructing a property file for javascript, I did this.

In JSP page :
<c:set var="list_size" value="${list1.size() }"></c:set>
Access this value in Javascipt page using :
var list_size = parseInt($('#list_size').val());
I added javascript page in my project externally.

Assign a raw HTML tag to a JavaScript variable

I'm working on an existing ASP.Net application and came across an interesting piece of JavaScript that I've been wondering about.
A few variables are being declared as literals, and they aren't in strings. For example, something like this is done:
<script type="text/javascript">
var jsonData = <asp:Literal ID="MyJsonObject" runat="server" />;
......
</script>
And in the server side code(C#), these tags are actually being altered from a JsonTextWriter similarly to this:
var stringBuilder = new StringBuilder();
var stringWriter = new StringWriter(stringBuilder);
using (var jsonWriter = new JsonTextWriter(stringWriter))
{
jsonWriter.Formatting = Formatting.Indented;
jsonWriter.WriteStartObject();
jsonWriter.WritePropertyName("someProperty");
jsonWriter.WriteValue("someValue");
jsonWriter.WriteEndObject();
}
MyJsonObject.Value = stringBuilder.ToString();
This in turn is causing the jsonData variable to be able to be used as a Json object in the client side code.
What I've noticed is,
if I put single quotes around the tag and change it to:
<script type="text/javascript">
var jsonData = '<asp:Literal ID="MyJsonObject" runat="server" />';
......
</script>
This doesn't work as it's no longer coming across as a Json object, but as an actual string. However, as I would expect, when it's just a plain tag, I'm receiving several syntax errors from Visual Studio.
So my question is:
Is this something that's generally acceptable or should I avoid keeping things like this around? Yeah, it works, but it doesn't look right to me.
I've found a few different questions that seem to be related here, but none seem to provide any insight on my particular situation.

In short: Yes, this looks acceptable. That appears to be one of the intended use-cases of the <asp:Literal> tag. Since you're writing a Javascript object literal, you won't even need the single-quotes, since that will change how the code works.
The thing to note is that <asp:Literal> isn't an HTML tag, and therefore will not make it to the user as it is. The <asp:Literal> tag gets pre-processed by ASP.NET before the page is sent to the user (since you have runat="server" specified); therefore, it will be processed regardless of surrounding content and replaced entirely with the resolved string value. Thus, your rendered page will be transformed (on the server-side) from this:
var jsonData = <asp:Literal ID="MyJsonObject" runat="server" />;
to this:
var jsonData = {
"someProperty" : "someValue"
};
This is a good way of transferring rich data constructed on the server-side into the client-side Javascript without having to write out raw Javascript to the page.
If you wanted a JSON-formatted string instead, then doing what you're doing and calling JSON.stringify(jsonData) afterwards would be your best bet.

How can I insert JSON into a script tage in a zope chameleon template?

I am building a pyramid/python app where my view callable for a certain template passes in a value called data. This variable is an array in the form of [[[x1,y1,z1,],...],[[v1,v2,v3],...]]
in my viewcallable I have
import json
jsdata = json.dumps(data)
I want to put it into a javascript script tag section of my template so:
<script>
data=${jsdata}
</script>
but i'm pretty sure that syntax is incorrect. How can I do this?
Edit: from this: http://docs.pylonsproject.org/projects/pyramid/en/latest/narr/templates.html it seems that Genshi style replacements are the way to go, which I take to mean that what I have above is correct. I am still unsure however, about whether this should be treated differently because it is going inside a javascript tag. Is this true?

You want to insert a JavaScript array, not a Python list.
The easiest way to convert between Python and JavaScript formats is to use the json module. JSON is a JavaScript subset for data after all:
import json
jsdata = (json.dumps(data)
.replace(u'<', u'\\u003c')
.replace(u'>', u'\\u003e')
.replace(u'&', u'\\u0026')
.replace(u"'", u'\\u0027'))
then pass jsdata to your template instead. The str.replace() calls ensure that the data remains HTML safe.
In the template, interpolate this without escaping:
<script>
var data = ${structure:jsdata};
</script>

I'm not sure about Chameleon, but "classical" Zope Page Templates did not allow to do anything inside script tags - if you don't see your variables interpolated it is likely that Chameleon behaves the same. The reason for this, as I understand, is to avoid exactly this type of code generation (you're generating JavaScript from Python via the template). Also, ZPT is an XML-based templating language and the content of <script> tags does not have to be a valid XML.
To work around the problem, you could do something like
jsdata = '<script type="text/javascript">var data = ' + json.dumps(data) + ';</script>'
and in your template insert the whole thing:
<tal:myscript replace="structure jsdata" />
Alternatively, you could do something like
<tal:lt replace="string:<" />script>
var data = <tal:script replace="structure jsdata" />;
<tal:lt replace="string:<" />/script>
which would hide the script tags from Chameleon.
It would be a good practice to try to keep the amount of generated JavaScript in your pages as minimal as possible.