Normative: `Array.prototype.sort`: comparefn must be fn or undefined #785

ljharb · 2017-01-25T19:55:14Z

This requires implementations throw a TypeError when the compare function is neither undefined nor a function, which is currently vaguely implied but not explicitly required.

This reflects web reality in that every engine except v8 already throws in this case. (Safari does not, but Safari TP and webkit latest do)

eshost output of [1, 2].sort(true):

┌─────────────────────┬─────────────────────────────────────────────────────────────────────────────────────────────┐
│ chakra              │                                                                                             │
│ chakra-es6          │ TypeError: Array.prototype.sort: argument is not a JavaScript object                        │
│ chakra-experimental │                                                                                             │
├─────────────────────┼─────────────────────────────────────────────────────────────────────────────────────────────┤
│ d8                  │ 1,2                                                                                         │
│ d8 harmony          │                                                                                             │
├─────────────────────┼─────────────────────────────────────────────────────────────────────────────────────────────┤
│ sm                  │                                                                                             │
│                     │ TypeError: invalid Array.prototype.sort argument                                            │
├─────────────────────┼─────────────────────────────────────────────────────────────────────────────────────────────┤
│ jsc                 │                                                                                             │
│                     │ TypeError: Array.prototype.sort requires the comparsion function be a function or undefined │
└─────────────────────┴─────────────────────────────────────────────────────────────────────────────────────────────┘

This will likely need "web reality" and "needs consensus" labels.

This requires implementations throw a `TypeError` when the compare function is neither undefined nor a function, which is currently vaguely implied but not explicitly required. This reflects web reality in that every engine except v8 already throws in this case.

mathiasbynens · 2017-01-25T20:30:42Z

spec.html

@@ -30780,6 +30780,7 @@
        <emu-alg>
          1. Let _obj_ be ? ToObject(*this* value).
          1. Let _len_ be ? ToLength(? Get(_obj_, `"length"`)).
+          1. If _comparefn_ is not *undefined* and IsCallable(_comparefn_) is *false*, throw a *TypeError* exception.


This could be step 1 instead of step 3, since the other steps aren’t needed in case we throw.

Or have you tested the order in which existing implementations (except for V8) execute these steps?

It seems SpiderMonkey and ChakraCore check comparefn first. Other engines check ToObject(this) first.

$ eshost -e 'Array.prototype.sort.call(null, null)' #### JavaScriptCore TypeError: Array.prototype.sort requires that |this| not be null #### ChakraCore TypeError: Array.prototype.sort: argument is not a JavaScript object #### SpiderMonkey TypeError: invalid Array.prototype.sort argument #### V8 TypeError: Array.prototype.sort called on null or undefined #### V8 Harmony TypeError: Array.prototype.sort called on null or undefined

Since in Firefox, Array.prototype.sort.call(null) throws "TypeError: can't convert null to object" but Array.prototype.sort.call(null, true) throws "TypeError: invalid Array.prototype.sort argument", this matches web reality. Changing now.

aha, thanks for the full comparison :-) I think since more engines agree on your change, that it's still the correct way to go. Updated!

For v8, it’s quite normal that it throws on ToObject(this), since it doesn’t throw on comparefn at all. (~~Still, I also prefer JSC behaviour over SpiderMonkey/Chakra one.~~ ... nevermind)

I'm ambivalent over whether the ToObject check or the IsCallable check comes first, but I think both should happen before the ToLength check.

GitHub was hiding this part here. I'm also glad this is placed before the get length operation. +1 for this change.

ariya · 2017-01-27T11:33:32Z

escope output

Did you mean eshost ?

ljharb · 2017-01-27T16:15:50Z

@ariya thanks, fixed

bterlson · 2017-02-01T21:35:25Z

I'm on board with this but let's wait to hear from our v8 friends.

ajklein · 2017-02-07T00:09:31Z

This seems reasonable to me, though this seems like a fairly low-leverage tightening of Array.prototype.sort given what's still allowed by the spec.

ljharb · 2017-02-07T00:10:15Z

@ajklein baby steps!

evilpie · 2017-02-07T17:06:23Z

Btw, I just checked in SpiderMonkey and we allow [1].sort({}), so non-callable objects. Can you check how other engines behave there?

evilpie · 2017-02-07T17:11:57Z

Turns out we optimize for arrays with length <= 1 so we never try to call the sort function in that case. We will still fail for [1, 2].sort({}). So this change is probably still fine from our side.

ljharb · 2017-02-07T17:15:46Z

I think most engines probably choose not to call the sorting function for < 2 elements; I'll look into that in a separate PR :-)

claudepache · 2017-02-07T18:49:21Z

Firefox seems to accept a-priori non-callable objects (but not primitives) as sort function but throws when attempting to use them. Safari TP has also an interesting behaviour:

testcase	Chrome Safari 10	Safari TP	Firefox	Edge
`[1].sort(_ => { throw new Error })`	`[1]`	`[1]`	`[1]`	`[1]`
`[1].sort({})`	`[1]`	`[1]`	`[1]`	TypeError
`[1].sort(2)`	`[1]`	`[1]`	TypeError	TypeError
`[1,2].sort(_ => { throw new Error })`	Error	Error	Error	Error
`[1,2].sort({})`	`[1,2]`	TypeError	TypeError	TypeError
`[1,2].sort(2)`	`[1,2]`	TypeError	TypeError	TypeError

(I vote for Edge semantics.)

…ined This requires implementations throw a `TypeError` when the compare function is neither undefined nor a function, which is currently vaguely implied but not explicitly required.

…a non-undefined non-function Per tc39/ecma262#785

ljharb · 2017-06-10T20:20:13Z

I updated to add a commit making the same change in TypedArray.prototype.sort.

test262 tests are here

bterlson · 2017-06-12T19:03:37Z

Thank you @ljharb! I will pull this now that tests are pending on test262.

…a non-undefined non-function (#1059) Per tc39/ecma262#785

This patch ensures a `TypeError` is thrown when the argument passed to `Array.prototype.sort` or `%TypedArray%.prototype.sort` is neither a function nor `undefined`. Every other major JavaScript engine already threw in this case. Making V8’s behavior match increases interoperability. tc39/ecma262#785 BUG=v8:6542 Cq-Include-Trybots: master.tryserver.v8:v8_linux_noi18n_rel_ng Change-Id: I412a59810abdd118217c8d8361389ec6c2f640bd Reviewed-on: https://chromium-review.googlesource.com/668356 Commit-Queue: Mathias Bynens <mathias@chromium.org> Reviewed-by: Yang Guo <yangguo@chromium.org> Cr-Commit-Position: refs/heads/master@{#48028}

mathiasbynens reviewed Jan 25, 2017

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ljharb force-pushed the sort_throws branch from 824e084 to 3f9dd80 Compare January 25, 2017 20:52

ljharb mentioned this pull request Jan 25, 2017

[1, 2].sort({}) has unhelpful error message chakra-core/ChakraCore#2411

Closed

bterlson added needs consensus This needs committee consensus before it can be eligible to be merged. web reality labels Feb 1, 2017

ljharb force-pushed the sort_throws branch from 3f9dd80 to f4ab016 Compare February 9, 2017 00:45

ljharb force-pushed the sort_throws branch from f4ab016 to 23daf37 Compare April 22, 2017 04:54

rwaldron added has consensus This has committee consensus. needs test262 tests The proposal should specify how to test an implementation. Ideally via github.com/tc39/test262 labels May 25, 2017

ljharb force-pushed the sort_throws branch from 23daf37 to a3559ce Compare May 27, 2017 03:21

ljharb removed the needs consensus This needs committee consensus before it can be eligible to be merged. label Jun 10, 2017

Normative: TypedArray.prototype.sort: comparefn must be fn or undef…

f0ee1d2

…ined This requires implementations throw a `TypeError` when the compare function is neither undefined nor a function, which is currently vaguely implied but not explicitly required.

ljharb force-pushed the sort_throws branch from a3559ce to f0ee1d2 Compare June 10, 2017 20:10

ljharb added a commit to ljharb/test262 that referenced this pull request Jun 10, 2017

Array.prototype.sort and %TypedArray%.prototype.sort should throw on …

82182f6

…a non-undefined non-function Per tc39/ecma262#785

ljharb mentioned this pull request Jun 10, 2017

{Array,%TypedArray%}.prototype.sort should throw on a non-undefined non-function tc39/test262#1059

Merged

ljharb added the normative change Affects behavior required to correctly evaluate some ECMAScript source text label Jun 10, 2017

bterlson merged commit 564b30b into tc39:master Jun 12, 2017

ljharb deleted the sort_throws branch June 12, 2017 19:20

leobalter pushed a commit to tc39/test262 that referenced this pull request Jun 12, 2017

Array.prototype.sort and %TypedArray%.prototype.sort should throw on …

f1c1b33

…a non-undefined non-function (#1059) Per tc39/ecma262#785

rwaldron added has test262 tests and removed needs test262 tests The proposal should specify how to test an implementation. Ideally via github.com/tc39/test262 labels Jun 22, 2017

ljharb mentioned this pull request Sep 19, 2017

Move the Array.prototype.sort comparefn test away from /es5/ compat-table/compat-table#1176

Open

Jamesernator mentioned this pull request Nov 12, 2017

[Meta] Should ECMA262 pull requests be listed here or just as issues on the main repository? babel/proposals#33

Open

claudepache mentioned this pull request Nov 15, 2017

Array#sort with non-function argument: add tests for arrays with less than 2 elements tc39/test262#1345

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Normative: `Array.prototype.sort`: comparefn must be fn or undefined #785

Normative: `Array.prototype.sort`: comparefn must be fn or undefined #785

ljharb commented Jan 25, 2017 •

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Normative: Array.prototype.sort: comparefn must be fn or undefined #785

Normative: Array.prototype.sort: comparefn must be fn or undefined #785

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Normative: `Array.prototype.sort`: comparefn must be fn or undefined #785

Normative: `Array.prototype.sort`: comparefn must be fn or undefined #785

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