The Ember Handlebars precompiler throws an error when using variables beginning with '@'

[stephendeyoung]

In Handlebars templates you should be able to use a variable beginning with @. Handlebars itself provides the @index variable inside an #each block. However, using any variable beginning with @ such as @index or any other variable you might define using a Handlebars helper will throw an error:

SyntaxError: Unexpected token ,
at Object.Function (<anonymous>)
at Object.JavaScriptCompiler.createFunctionContext (http://localhost:9292/handlebars.js:1500:23)
at Object.JavaScriptCompiler.compile (http://localhost:9292/handlebars.js:1415:17)
at Object.Ember.Handlebars.precompile (ember-handlebars-compiler:247:52)
at Object.templateString (ember-handlebars/~tests/handlebars_test:1812:41)
at Object.Test.run (http://localhost:9292/qunit/qunit.js:190:18)
at http://localhost:9292/qunit/qunit.js:348:10
at process (http://localhost:9292/qunit/qunit.js:1420:24)
at http://localhost:9292/qunit/qunit.js:466:5

Using the ordinary Handlebars precompiler does not throw an error when you try to use an @ variable.

You can see the @index error here and the custom variable error here. This pull request includes two failing unit tests.

[wycats]

This is really a request to support helper-supplied data variables in Ember, which is on the docket.

[itsjavi]

@wycats I didn't found the feature request post talking about this, but I think, in my humble opinion, array indexes are a very essential part of programming and therefore this issue should be considered a bug and not a feature request ;)
I tried to see the ember.js source to figure out which lines causes this bug, but I think that is more complicated than a few lines, so I trust in the ember team to fix this for the 1.0 release, if possible ;) (i can see that it is planned for that release but the issue is closed...)

[itsjavi]

I've found a temporary solution by using {{_view.contentIndex}}
http://jsfiddle.net/SRKD5/2/

[chrisvariety]

@xaguilars you can always calculate this index yourself, e.g.

{{#each object in collection}}
  Index: {{index object collection}}
{{/each}}

Ember.Handlebars.registerBoundHelper('index', function(objectInCollection, collection) {
  return collection.indexOf(objectInCollection);
});

[itsjavi]

@speedmanly nice example, but won't this impact in the performance of the app as it have to seek for the index each time in the loop?

[chrisvariety]

Definitely, but I'm not sure how much it would really matter unless your
arrays are super large. Profile it & find out ! :)

On Saturday, August 31, 2013, Javier Aguilar wrote:

@speedmanly https://github.com/speedmanly nice example, but won't this
impact in the performance of the app as it have to seek for the index each
time in the loop?

—
Reply to this email directly or view it on GitHubhttps://github.com//pull/3030#issuecomment-23618232
.

[dfreeman]

@wycats Is support for helper-exposed data still on the docket for a future Ember release? Attempting to reference such variables in a template still appears to cause a syntax error when compiling the resulting function string.

[blessanm86]

Is there any update for the helper-supplied data variables feature?