The Tor Browser / file revision

 // for-of does not trigger the JS 1.7 for-in destructuring special case.

 version(170);

 var data = [[1, 2, 3], [4, 5, 6, 7]];

 function test(vars, expr, result) {

     var s = '';

     eval("for (" + vars + " of data) s += (" + expr + ") + ';';");

     assertEq(s, result);

 }

 for (var prefix of ["var ", "let ", ""]) {

     test(prefix + "[a, b, c]",

          "a + ',' + b + ',' + c",

          "1,2,3;4,5,6;");

 }

 test("var [a]", "a", "1;4;");

 test("var {length: len}", "len", "3;4;");

 test("var {length}", "length", "3;4;");

 test("{}", "0", "0;0;");