I think I found a bug: Miniracer crashes with valid ES6 syntax

Development

AI-generated summary

A bug has been reported where Miniracer crashes when compiling valid ES6 syntax. sukima shared an example of code that causes the issue, using computed property names in an object initializer. Despite being valid according to the ES2015 specs, Miniracer throws an error. sam suggested that the issue may be due to Miniracer not receiving transpiled JavaScript from Babel, as the code is not being transpiled before being processed by Miniracer.

1

This is quite frustrating and I’d love to understand how historically this has happened.

If I write the following valid ES6 code into discourse/services/foo.js.es6 and add it to the asset pipeline in Discourse it will fail to compile:

const FOO = 'foo';
export default Ember.Service.extend({
  [FOO]() {
    console.log('This should work');
  }
});

But alas I get:

Bundling assets
** Execute assets:precompile
rake aborted!
MiniRacer::RuntimeError: Error: Line 3: Unexpected token [
JavaScript at throwError (<anonymous>:2581:21)
JavaScript at throwUnexpected (<anonymous>:2643:9)
JavaScript at parseObjectProperty (<anonymous>:2914:17)
JavaScript at <anonymous>:5663:38
JavaScript at parseObjectInitialiser (<anonymous>:2943:24)
JavaScript at parsePrimaryExpression (<anonymous>:3082:20)
JavaScript at <anonymous>:5663:38
JavaScript at trackLeftHandSideExpressionAllowCall (<anonymous>:5565:61)
JavaScript at parsePostfixExpression (<anonymous>:3216:20)
JavaScript at <anonymous>:5663:38
/opt/bitnami/apps/discourse/htdocs/vendor/bundle/ruby/2.3.0/gems/mini_racer-0.1.9/lib/mini_racer.rb:168:in `eval_unsafe'
/opt/bitnami/apps/discourse/htdocs/vendor/bundle/ruby/2.3.0/gems/mini_racer-0.1.9/lib/mini_racer.rb:168:in `block (2 levels) in eval'
/opt/bitnami/apps/discourse/htdocs/vendor/bundle/ruby/2.3.0/gems/mini_racer-0.1.9/lib/mini_racer.rb:239:in `timeout'
/opt/bitnami/apps/discourse/htdocs/vendor/bundle/ruby/2.3.0/gems/mini_racer-0.1.9/lib/mini_racer.rb:167:in `block in eval'
/opt/bitnami/apps/discourse/htdocs/vendor/bundle/ruby/2.3.0/gems/mini_racer-0.1.9/lib/mini_racer.rb:64:in `block in with_lock'
/opt/bitnami/apps/discourse/htdocs/vendor/bundle/ruby/2.3.0/gems/mini_racer-0.1.9/lib/mini_racer.rb:64:in `synchronize'
/opt/bitnami/apps/discourse/htdocs/vendor/bundle/ruby/2.3.0/gems/mini_racer-0.1.9/lib/mini_racer.rb:64:in `with_lock'
/opt/bitnami/apps/discourse/htdocs/vendor/bundle/ruby/2.3.0/gems/mini_racer-0.1.9/lib/mini_racer.rb:165:in `eval'

I know this is valid syntax as babel and ember-cli handle this just fine. The ES2015 specs (§12.2.6) even discuss it.

I have also tried this syntax:

{
  [dynamicMethodName]: function() {}
}

And it too has the same error.

2

Well we appear not to be traspiling it, miniracer gets transpiled js from Babel