one-var reports error for a variable declared in a for-loop after an uninitialized variable declaration

What version of ESLint are you using? v2.5.3

What parser (default, Babel-ESLint, etc.) are you using? default

Please show your full configuration:

{
  "rules": {
    "one-var": ["error", {
      "initialized": "never",
      "uninitialized": "always"
    }]
  }
}

What did you do? Please include the actual source code causing the issue.

Here is a small code snippet reproducing my issue. Just save it to a file and run eslint with the config shown above.

function reproduce(candidates) {
  var err;
  for (var ix in candidates) {
    err = ix > 0;
  }
  console.log(err);
}

What did you expect to happen?

The code should pass linter checks.

What actually happened? Please include the actual, raw output from ESLint.

$ eslint bug.js

/private/tmp/bug/bug.js
  3:8  error  Combine this with the previous 'var' statement with uninitialized variables  one-var

✖ 1 problem (1 error, 0 warnings)

As far as my understanding goes, eslint considers the ix variable declared inside for loop as unitialized and therefore complains that it should have been defined on the same line as the err variable (before the for loop). Indeed, the following code passes the checks:

function reproduce(candidates) {
  var err, ix;
  for (ix in candidates) {
    err = ix > 0;
  }
  console.log(err);
}

From my point of view, I am proposing one of the following two changes:

• Fix the implementation of one-var to treat for loop variables differently.
• Add an one-var option similar to init-declaration's ignoreForLoopInit that will tell one-var to treat variables defined in for-loops differently.

Thoughts?

[ilyavolodin]

@bajtos That looks like the right place. I verified that the rule doesn’t warn for regular for loop statements, only for for...in and for...of, so it sounds like you just need to add those as special case along with ForStatement. And yes, tests would go into the file you linked.

[mysticatea]

I don’t understand this thread completely, but I think variable declarations at ForInStatement.left and ForOfStatement.left should be treated as initialized. Those variables will be initialized with iteration items.