#4356 — Iteration statements return undefined instead of empty

bug_id: 4356
creation_ts: 2015-05-07 06:47:00 -0700
short_desc: Iteration statements return undefined instead of empty
delta_ts: 2015-05-07 09:05:40 -0700
product: Draft for 6th Edition
component: normative change from ES5.x
version: Rev 38: April 14, 2015 Final Draft
rep_platform: All
op_sys: All
bug_status: RESOLVED
resolution: INVALID
priority: Normal
bug_severity: major
everconfirmed: true
reporter: manish.tripathi.777
assigned_to: Allen Wirfs-Brock
cc: andrebargull

commentid: 14384
comment_count: 0
who: manish.tripathi.777
bug_when: 2015-05-07 06:47:45 -0700

All iteration statements and if statement return "undefined" value when their body is not evaluated, which is not consistent with ES5.1, example:

1; while (false) ;

should evaluate to 1 according to ES5.1, but according to current specification of ES6 will evaluate to "undefined".

The is caused by initializing V to "undefined" in ES6 versus "empty" in ES5.1, for example see ES6 final draft (http://wiki.ecmascript.org/lib/exe/fetch.php?id=harmony%3Aspecification_drafts&cache=cache&media=harmony:ecma-262_6th_edition_final_draft_-04-14-15-markup.pdf) - 13.7.3.6, item 1 - Let V=undefined
but in ES5.1 final draft (http://www.ecma-international.org/publications/files/ECMA-ST/Ecma-262.pdf) - 12.6.1, item 1 - Let V=empty

commentid: 14388
comment_count: 1
who: André Bargull
bug_when: 2015-05-07 07:23:43 -0700

This is an intentional change from ES5 based on the completion reform proposal: http://wiki.ecmascript.org/doku.php?id=harmony:completion_reform

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#4356 — Iteration statements return undefined instead of empty