An unexpected behaviour in strict mode in PhantomJS

[aleen42]

Recently, I have found that when I upgraded core-js, a test case run in PhantomJS had failed with the following exception:

PhantomJS 2.1.1 (Mac OS 0.0.0) LOG: 'polyfill load failed', ReferenceError: Can't find variable: SAFE_CLOSING
exports
eval code
eval@[native code]
./node_modules/core-js/modules/es.array.from.js@http://localhost:9876/base/build/coremail/__karma__bundle/commons.js?407226f1f29b0c48cbb273c58df7aaa58a0e970e:3027:5
__webpack_require__@http://localhost:9876/base/build/coremail/__karma__bundle/runtime.js?3c2a1c270c4c70b6d7720b608d8bc64728c3bd1b:31:46

To trace the source, I have found that the behaviour existed due to the commit 11f4ec8, which specified check-correctness-of-iteration.js to execute in strict mode.

'use strict';
var wellKnownSymbol = require('../internals/well-known-symbol');

var ITERATOR = wellKnownSymbol('iterator');
var SAFE_CLOSING = false;

try {
  var called = 0;
  var iteratorWithReturn = {
    next: function () {
      return { done: !!called++ };
    },
    'return': function () {
      SAFE_CLOSING = true;
    }
  };
  iteratorWithReturn[ITERATOR] = function () {
    return this;
  };
  // eslint-disable-next-line es/no-array-from, no-throw-literal -- required for testing
  Array.from(iteratorWithReturn, function () { throw 2; });
} catch (error) { /* empty */ }

module.exports = function (exec, SKIP_CLOSING) {
  if (!SKIP_CLOSING && !SAFE_CLOSING) return false; // Can't find variable: SAFE_CLOSING
  // ...
}

After a simple trial, I found that the execution of the following snippet has broken the scope:

Array.from(iteratorWithReturn, function () { throw 2; });