jest 0.5.x: eval strict function and new expression

[DmitrySoshnikov]

With vm.runInContext and jsdom 5.4.3, we started to get ReferenceError issues:

describe('strict eval', function() {
  it('eval', function() {
    var code = [
      'var _bar = 10;',
      'function foo() {',
      '  "use strict";', // because of this
      '  return _bar;',
      '}',
    ].join('\n');

    eval(code);

    new foo(); // Reference error: _bar is not defined
  });
});

Thus it relates only to "use strict" inside the function, without it, _bar is available in the new foo() call.

The vm.runInContext seems works fine in isolation in this case. Can be jsdom related?

CC @ide, @domenic

[DmitrySoshnikov]

OK, it's nevertheless issue of vm.runInContext. If a code is wrapped into a function, then evaling strict function inside that function, doesn't capture the bindings.

This works (file test.js):

var code = `
var foo = {m: 1};

function bar() {
  "use strict";
  return foo;
}
`;

eval(code);

bar();

Node session:

> vm.runInNewContext(fs.readFileSync('/Users/dmitrys/test.js', 'utf-8'))
{ m: 1 }
>

This doesn't:

function main() {

  var code = `
    var foo = {m: 1};

    function bar() {
      "use strict";
      return foo;
    }
  `;

  eval(code);

  bar(); // foo is not defined

}

main();

Node session:

> vm.runInNewContext(fs.readFileSync('/Users/dmitrys/test.js', 'utf-8'))
undefined:6
      return foo;
             ^
ReferenceError: foo is not defined
    at bar (eval at main (evalmachine.<anonymous>:13:8), <anonymous>:6:14)
    at main (evalmachine.<anonymous>:15:3)
    at evalmachine.<anonymous>:19:1
    at ContextifyScript.Script.runInNewContext (vm.js:18:15)
    at Object.exports.runInNewContext (vm.js:49:17)
    at repl:1:4
    at REPLServer.defaultEval (repl.js:154:27)
    at bound (domain.js:254:14)
    at REPLServer.runBound [as eval] (domain.js:267:12)
    at REPLServer.<anonymous> (repl.js:308:12)

Unless I'm missing something obvious from strict mode, it's probably a bug in vm module, and is not related to Jest or jsdom.

[ide]

The exact same script source is passed to vm.runInContext and jsdom's evaluator: https://github.com/facebook/jest/blob/0.5.x/src/JSDomEnvironment.js#L110 and https://github.com/facebook/jest/blob/0.5.x/src/JSDomEnvironment.js#L132. And looking how jsdom evaluate scripts, it also uses vm.runInContext.

I repro'd your latest results where the same error occurs with both vm.runInContext and jsdom, even with plain function calls without new.

Another thing I noticed was that after the eval call, expect(_bar).toBe(10) throws an error since _bar is not defined. So either the eval is acting as some kind of indirect eval or it is using a different global scope.

[DmitrySoshnikov]

Need to notice, this is test form io.js v2.3.1. With Node v.0.12 the vm.runInContext has even different behavior: the bar is not defined there.

Also, if no "strict mode" is used, then the foo is captured in bar.

[DmitrySoshnikov]

OK, I filed this issue on io.js yet: nodejs/node#2245, hope we'll get some clarifications. Though, it's currently a blocker for us at Facebook to switch to Jest 0.5 with io.js (CC @yungsters), and probably will be a blocker to merge 0.5 to master on August 1st as we planned.

[cpojer]

This seems like it was fixed in node 4.

[github-actions]

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