What is the proper way to check for existence of variable in an EJS template (using ExpressJS)?-Collection of common programming errors

2 years ago
admin
2 minutes

On the EJS github page, there is one and only one simple example: https://github.com/visionmedia/ejs

Example

This seems to be checking for the existence of a variable named user, and if it exists, do some stuff. Duh, right?

My question is, why in the world would Node throw a ReferenceError if the user variable doesn't exist? This renders the above example useless. What's the appropriate way to check for the existence of a variable? Am I expected to use a try/catch mechanism and grab that ReferenceError?

ReferenceError: user is not defined
    at IncomingMessage.anonymous (eval at  (/usr/local/lib/node/.npm/ejs/0.3.1/package/lib/ejs.js:140:12))
    at IncomingMessage. (/usr/local/lib/node/.npm/ejs/0.3.1/package/lib/ejs.js:142:15)
    at Object.render (/usr/local/lib/node/.npm/ejs/0.3.1/package/lib/ejs.js:177:13)
    at ServerResponse.render (/usr/local/lib/node/.npm/express/1.0.7/package/lib/express/view.js:334:22)
    at Object. (/Users/me/Dropbox/Projects/myproject/server.js:188:9)
    at param (/usr/local/lib/node/.npm/connect/0.5.10/package/lib/connect/middleware/router.js:146:21)
    at pass (/usr/local/lib/node/.npm/connect/0.5.10/package/lib/connect/middleware/router.js:162:10)
    at /usr/local/lib/node/.npm/connect/0.5.10/package/lib/connect/middleware/router.js:152:27
    at Object.restrict (/Users/me/Dropbox/Projects/myproject/server.js:94:5)
    at param (/usr/local/lib/node/.npm/connect/0.5.10/package/lib/connect/middleware/router.js:146:21)

I understand that I could make this error go away by simply adding a “user” local variable in my server code, but the whole point here is that I want to check for the existence of such variables at runtime using your every day if/else nullcheck type pattern. An exception for a variable that doesn’t exist seems ridiculous to me.

  1. how you would with anything in js, typeof foo == ‘undefined’, or since “locals” is the name of the object containing them, you can do if (locals.foo). it’s just raw js :p

Originally posted 2013-11-09 21:44:08.