node.js - Pass variables to JavaScript in ExpressJS -

i lost on this; using nodejs fetch json , need pass variable page , have javascript use data.

app.get('/test', function(req, res) {     res.render('testpage', {         myvar: 'my data'     }); 

that express code (very simple testing purposes); using ejs want gather data know render on page simply

<%= myvar %> 

but need able gather data in javascript (if possible within .js file) display variable in alert box have tried

in jade alert('!{myvar}') or !{json.stringify(myvar)}. can similar in ejs. don't need field <input type=hidden> , taking value of field in javascript. if can appreciated

you use (client-side):

<script>   var myvar = <%- json.stringify(myvar) %>; </script> 

you ejs render .js file:

app.get('/test.js', function(req, res) {   res.set('content-type', 'application/javascript');   res.render('testpage', { myvar : ... }); }); 

however, template file (testpage) still need have .html extension, otherwise ejs won't find (unless tell express otherwise).

as @ksloan points out in comments: have careful myvar contains. if contains user-generated content, may leave site open script injection attacks.

a possible solution prevent happening:

<script>   function htmldecode(input){     var e = document.createelement('div');     e.innerhtml = input;     return e.childnodes.length === 0 ? "" : e.childnodes[0].nodevalue;   }   var myvar = json.parse(htmldecode("<%= json.stringify(myvar) %>")); </script>