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Leaking state in program scope #446

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MichalBryxi opened this issue Jul 3, 2019 · 2 comments · May be fixed by #447
Closed

Leaking state in program scope #446

MichalBryxi opened this issue Jul 3, 2019 · 2 comments · May be fixed by #447

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@MichalBryxi
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Consider following service:

var cachedFoo = null;

export default Service.extend({
  fetchFoo(count) {
    if(!cachedFoo) {
      fetch(`./api/?results=${count}`).then(function(response) {
        cachedFoo = response;
      });
    }
  }

  getFoo() {
    return cachedFoo;
  }
});

This service will probably work as expected in the scope of running Ember code.

But if there are two tests calling this service with different value for count when calling fetchFoo, then calls to getFoo will always return the response of the first test.
@MichalBryxi MichalBryxi mentioned this issue Jul 3, 2019
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@MichalBryxi
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This just bit us in our test code, so I thought an eslint rule might be a good idea.

I know that just enforcing consts is not bullet-proof as the content of an object can be still mutated, but forcing user to use const instead of var or let might give them a hint that something might be wrong.

  • This is my first eslint rule, so not really sure what I might have missed.
  • Also not sure whether there might be files that actually can have global mutable variables without compromising the tests.

@rajasegar
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@MichalBryxi FYI
https://eslint.org/docs/rules/prefer-const
https://eslint.org/docs/rules/no-var

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Add new rule no-leaking-state-in-program-scope MichalBryxi/eslint-plugin-ember
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@MichalBryxi @rajasegar