util: support inspecting Map, Set, and Promise #1471

monsanto · 2015-04-20T00:58:46Z

Among other things, this makes working with ES6 containers bearable on the REPL.

Before:

> new Map([[1, "foo"], [null, "bar"], [{quux: 42}, undefined]])
{}

After:

> new Map([[1, "foo"], [null, "bar"], [{quux: 42}, undefined]])
Map { 1 => 'foo', null => 'bar', { quux: 42 } => undefined }

The output format is inspired by Chrome DevTools.

I would like to support inspecting promises but I do not know of a way to synchronously obtain the status and fulfillment value. If someone would like to point me in the right direction I can provide a followup PR. (see below)

The output format is inspired by Chrome DevTools.

domenic · 2015-04-20T02:00:24Z

I would like to support inspecting promises but I do not know of a way to synchronously obtain the status and fulfillment value.

Probably only possible via the V8 API... would be worth looking at the dev tools code to see how it's done

domenic · 2015-04-20T02:01:22Z

lib/util.js

+ // If the opening "brace" is too large, like in the case of "Set {",
+ // we need to force the first item to be on the next line or the
+ // items will not line up correctly.
+ (base === '' && braces[0].length === 1 ? '' : base + '\n ') +


Seems like this case needs tests

brendanashworth · 2015-04-20T03:09:17Z

test/parallel/test-util-inspect.js

@@ -235,3 +235,17 @@ if (typeof Symbol !== 'undefined') {
 assert.equal(util.inspect(subject, options), '[ 1, 2, 3, [length]: 3, [Symbol(symbol)]: 42 ]');

 }
+
+// test Set
+assert.equal(util.inspect(new Set), 'Set {}')


style: semicolons here and below

I have that in a new commit yet to be pushed. Is it normal that make jshint doesn't touch tests?

Yeah, for some reason that choice was made a long time ago. Wouldn't call it "normal" though :)

monsanto · 2015-04-20T03:36:34Z

@domenic I have added a test covering the case you commented on, thanks.

There were no tests of alignment at all, so I took the luxury of adding tests for the rest of the containers as well.

monsanto · 2015-04-20T07:21:53Z

I just pushed a proof-of-concept implementation of util.inspect for Promises. It uses the mirror debugger to synchronously inspect Promises. (Alternatively, this could be done if I could have a module with compiler intrinsics enabled). There are bits I don't like about my implementation but I wanted to get this out there before I went to bed in case people think my course of action totally sucks and I should abandon ship 😛

Output looks like

> Promise.resolve(3)
Promise { 3 }
> Promise.reject(3)
Promise { <rejected> 3 }
> new Promise(function(){})
Promise { <pending> }

which is a change from Chrome DevTools, as they are ridiculously verbose:

> Promise.resolve(3)
Promise {[[PromiseStatus]]: "resolved", [[PromiseValue]]: 3}
> Promise.reject(3)
Promise {[[PromiseStatus]]: "rejected", [[PromiseValue]]: 3}
> new Promise(function(){})
Promise {[[PromiseStatus]]: "pending", [[PromiseValue]]: undefined}

bnoordhuis · 2015-04-20T09:35:28Z

Left some comments on the promise inspection code. I don't disagree with the Debug.MakeMirror approach (in fact I think it's the only way to crack open a promise) but I think the current implementation is creating mirrors too eagerly.

monsanto · 2015-04-20T21:39:11Z

@bnoordhuis Thank you for your comments.

runInDebugContext isn't cheap

I've hoisted it to the top of the file for simplicity; however if this is too expensive or otherwise unsatisfactory I can create it on demand and cache.

only way to crack open a promise

If we could have compiler intrinsics enabled for the lib/internals folder, the Promise internals are at the properties %CreateGlobalPrivateOwnSymbol("Promise#status") and ...("Promise#value"). I don't know if this is more or less desirable than using runInDebugContext. My guess is less, but perhaps this functionality would be useful for other things in the future..

Mirrors being cached

you are correct, I should have noticed this. They are now created as "transient" so they will not be cached.

creating so many mirrors

I've guarded the mirror creation with an instanceof, so the common case should not be penalized. The code still calls inspectPromise twice if it is indeed a native promise, but I can't eliminate this without a more involved refactor (or creating a closure, which seems just as bad as creating an extra mirror). I have tried to keep my changes as minimal as possible as this is my first io.js PR.

we may mutate keys in the typecase, so don't check keys.length until no more mutations.

chrisdickinson · 2015-04-22T21:25:53Z

lib/util.js

@@ -1,6 +1,7 @@
 'use strict';

 const uv = process.binding('uv');
+const Debug = require('vm').runInDebugContext('Debug');


@domenic: Should we add support for Weak{Set,Map} inspection through Debug as a follow-on to this PR?

Noooo that seems very bad, basically exposes iteration to JS.

Yeah – I thought it might be a bit fraught with peril; was surprised to see the chrome dev tools expose that info.

chrisdickinson · 2015-04-22T21:35:18Z

The nits can probably be disregarded – just looked and saw that we were using map before, anyway :)

This LGTM. Unless @bnoordhuis or @domenic objects, I'll merge this tomorrow afternoon.

bnoordhuis · 2015-04-23T10:38:07Z

If we could have compiler intrinsics enabled for the lib/internals folder, the Promise internals are at the properties %CreateGlobalPrivateOwnSymbol("Promise#status") and ...("Promise#value").

It's possible to do that but it's kind of a hack:

const v8 = require('v8');
v8.setFlagsFromString('--allow_natives_syntax');
const promiseStatus = eval('%CreateGlobalPrivateOwnSymbol("Promise#status")');
const promiseValue = eval('%CreateGlobalPrivateOwnSymbol("Promise#value")');
v8.setFlagsFromString('--noallow_natives_syntax');

bnoordhuis · 2015-04-23T10:41:56Z

lib/util.js

@@ -276,14 +285,44 @@ function formatValue(ctx, value, recurseTimes) {
 }
 }

- var base = '', array = false, braces = ['{', '}'];
+ var base = '', empty, braces, formatter;


Preferably assign empty = false and use strict checks below (i.e. empty = empty === true && keys.length === 0 and if (empty === true) {.)

It's a minor thing but V8 emits marginally tighter code for strict boolean comparisons.

monsanto · 2015-04-23T15:18:18Z

@bnoordhuis @chrisdickinson OK, I addressed these style nits.

Just curious, is there a reason to keep the instanceof check out of inspectPromise?

It saves an instanceof check. I'm hoping to do a larger scale cleanup of util.inspect when I next have free time, which should fix the double inspectPromise calls and make this issue moot.

Aside: am I the only one who finds it moronic that recurseTimes is sometimes a number and sometimes not?

Yes, another thing I would like to clean up. (Or at least move the subtraction logic to a central place)

PR-URL: #1471 Reviewed-By: Chris Dickinson <christopher.s.dickinson@gmail.com>

chrisdickinson · 2015-04-26T02:20:21Z

Merged in bf7ac08. Thanks!

@othiym23

PR-URL: #1532 Notable Changes: * crypto: significantly reduced memory usage for TLS (Fedor Indutny & Сковорода Никита Андреевич) #1529 * net: socket.connect() now accepts a 'lookup' option for a custom DNS resolution mechanism, defaults to dns.lookup() (Evan Lucas) #1505 * npm: Upgrade npm to 2.9.0. See the v2.8.4 and v2.9.0 release notes for details. Notable items: - Add support for default author field to make npm init -y work without user-input (@othiym23) npm/npm/d8eee6cf9d - Include local modules in npm outdated and npm update (@ArnaudRinquin) npm/npm#7426 - The prefix used before the version number on npm version is now configurable via tag-version-prefix (@kkragenbrink) npm/npm#8014 * os: os.tmpdir() is now cross-platform consistent and will no longer returns a path with a trailling slash on any platform (Christian Tellnes) #747 * process: - process.nextTick() performance has been improved by between 2-42% across the benchmark suite, notable because this is heavily used across core (Brian White) #1548 - New process.geteuid(), process.seteuid(id), process.getegid() and process.setegid(id) methods allow you to get and set effective UID and GID of the process (Evan Lucas) #1536 * repl: - REPL history can be persisted across sessions if the NODE_REPL_HISTORY_FILE environment variable is set to a user accessible file, NODE_REPL_HISTORY_SIZE can set the maximum history size and defaults to 1000 (Chris Dickinson) #1513 - The REPL can be placed in to one of three modes using the NODE_REPL_MODE environment variable: sloppy, strict or magic (default); the new magic mode will automatically run "strict mode only" statements in strict mode (Chris Dickinson) #1513 * smalloc: the 'smalloc' module has been deprecated due to changes coming in V8 4.4 that will render it unusable * util: add Promise, Map and Set inspection support (Christopher Monsanto) #1471 * V8: upgrade to 4.2.77.18, see the ChangeLog for full details. Notable items: - Classes have moved out of staging; the class keyword is now usable in strict mode without flags - Object literal enhancements have moved out of staging; shorthand method and property syntax is now usable ({ method() { }, property }) - Rest parameters (function(...args) {}) are implemented in staging behind the --harmony-rest-parameters flag - Computed property names ({['foo'+'bar']:'bam'}) are implemented in staging behind the --harmony-computed-property-names flag - Unicode escapes ('\u{xxxx}') are implemented in staging behind the --harmony_unicode flag and the --harmony_unicode_regexps flag for use in regular expressions * Windows: - Random process termination on Windows fixed (Fedor Indutny) #1512 / #1563 - The delay-load hook introduced to fix issues with process naming (iojs.exe / node.exe) has been made opt-out for native add-ons. Native add-ons should include 'win_delay_load_hook': 'false' in their binding.gyp to disable this feature if they experience problems . (Bert Belder) #1433 * Governance: - Rod Vagg (@rvagg) was added to the Technical Committee (TC) - Jeremiah Senkpiel (@Fishrock123) was added to the Technical Committee (TC)

util: support inspecting Map and Set

613a63b

The output format is inspired by Chrome DevTools.

domenic reviewed Apr 20, 2015
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brendanashworth added the util Issues and PRs related to the built-in util module. label Apr 20, 2015

brendanashworth reviewed Apr 20, 2015
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(rebase) add semicolons to test

21e4e92

monsanto added 2 commits April 19, 2015 23:37

(rebase) check alignment of objects

87e36a6

(rebase) these semicolons are going to be the end of me

10d88e5

monsanto changed the title ~~util: support inspecting Map and Set~~ util: support inspecting Map, Set, and Promise Apr 20, 2015

util: support inspecting Promises

1185ff3

(rebase) promise fixes

c4d2cd0

(rebase) fix showHidden on empty set/map

ba53e97

we may mutate keys in the typecase, so don't check keys.length until no more mutations.

chrisdickinson reviewed Apr 22, 2015
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bnoordhuis reviewed Apr 23, 2015
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nits n stuff

79627ae

chrisdickinson pushed a commit that referenced this pull request Apr 26, 2015

util: add Map and Set inspection support

bf7ac08

PR-URL: #1471 Reviewed-By: Chris Dickinson <christopher.s.dickinson@gmail.com>

chrisdickinson closed this Apr 26, 2015

rvagg mentioned this pull request Apr 27, 2015

Release proposal: v2.0.0 #1532

Closed

monsanto deleted the map-set-inspect branch June 10, 2015 09:30

ofrobots mentioned this pull request Jul 25, 2015

util: delay creation of debug context #2248

Closed

lydell mentioned this pull request May 1, 2022

Truncate long Set and Map in util.inspect/console.log/REPL, just like long Array #42933

Closed

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util: support inspecting Map, Set, and Promise #1471

util: support inspecting Map, Set, and Promise #1471

monsanto commented Apr 20, 2015

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util: support inspecting Map, Set, and Promise #1471

util: support inspecting Map, Set, and Promise #1471

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