tc39/ecma262

Removal of Object type-check from GetIterator() algorithm

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#746 opened on Dec 6, 2016

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 (13 comments) (0 reactions) (0 assignees)HTML (15,626 stars) (1,409 forks)batch import
good first issueneeds consensusneeds specification text

Description

The If Type(iterator) is not Object, throw a TypeError exception. step is generally not implemented by engines, see https://jsfiddle.net/gj3uaw1t/ for an example. V8 does implement this step for yield*, but not other uses of GetIterator().

It would be cool if we could remove this from the spec and have common behaviour among implementations (it seems a recent version of SpiderMonkey has added the typecheck, breaking compatibility between FF and Chrome/Safari in this very unlikely situation).

Contributor guide

Tech stack
javascript
Domain
developer experience
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
under 1 hour
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
basic JavaScript knowledgefamiliarity with ECMAScript spec format
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
20
Research direction
The issue proposes removing the type check step in the GetIterator() algorithm from the ECMAScript specification. Look for the relevant section in the specification (likely in the 'ECMAScript Language: Iteration' part) and identify the exact line to delete. The comments indicate that most engines already omit this check, so the change aligns with common behavior. Ensure that the removal is consistent with the rest of the spec and update any related cross references if necessary.