Add flag to change `catch` variables' default types to `unknown` by DanielRosenwasser · Pull Request #41013 · microsoft/TypeScript · GitHub

This change adds a new flag called useUnknownInCatchVariables which changes the default type of catch clause variables from any (today's existing behavior) to unknown.

More specifically, under this flag, the following code

try {
  // ...
}
catch (err) {
  console.log(err.message);
}

would become equivalent to

try {
  // ...
}
catch (err: unknown) {
  console.log(err.message); // error: Property 'message' does not exist on type 'unknown'.
}

As a result, a user would receive the following error message from TypeScript:

Property 'message' does not exist on type 'unknown'.

To mitigate this, a user could explicitly perform runtime checks

try {
  // ...
}
catch (err) {
  // First check if we have an Error
  if (err instanceof Error) {
    console.log(err.message);
  }
}

or if that is too painful, a user could use a type assertion to any, or provide an explicit annotation on the catch clause variable with the type any to revert to the old default behavior.

try {
  // ...
}
catch (err: any) {
  console.log(err.message);
}

Fixes #41016.

The TypeScript team hasn't accepted the linked issue #41016. If you can get it accepted, this PR will have a better chance of being reviewed.

It would be awesome if strict also enabled this flag; is that likely? (It's possible that this change does that already; but I'm on my phone so it's hard to tell 😅)

TypeScript Bot (@typescript-bot) pack this
TypeScript Bot (@typescript-bot) test this
TypeScript Bot (@typescript-bot) user test this
TypeScript Bot (@typescript-bot) run dt
TypeScript Bot (@typescript-bot) perf test this

Heya Daniel Rosenwasser (@DanielRosenwasser), I've started to run the extended test suite on this PR at a32013b. You can monitor the build here.

Heya Daniel Rosenwasser (@DanielRosenwasser), I've started to run the parallelized Definitely Typed test suite on this PR at a32013b. You can monitor the build here.

Heya Daniel Rosenwasser (@DanielRosenwasser), I've started to run the parallelized community code test suite on this PR at a32013b. You can monitor the build here.

Heya Daniel Rosenwasser (@DanielRosenwasser), I've started to run the perf test suite on this PR at a32013b. You can monitor the build here.

Update: The results are in!

Heya Daniel Rosenwasser (@DanielRosenwasser), I've started to run the tarball bundle task on this PR at a32013b. You can monitor the build here.

Hey Daniel Rosenwasser (@DanielRosenwasser), I've packed this into an installable tgz. You can install it for testing by referencing it in your package.json like so:

{
    "devDependencies": {
        "typescript": "https://typescript.visualstudio.com/cf7ac146-d525-443c-b23c-0d58337efebc/_apis/build/builds/102337/artifacts?artifactName=tgz&fileId=CB39C963580F3F2B857D3171C4A6770212DE0222B86B618B209B2F4B2E12A36B02&fileName=/typescript-4.3.0-insiders.20210505.tgz"
    }
}

and then running npm install.

There is also a playground for this build and an npm module you can use via "typescript": "npm:@typescript-deploys/pr-build@4.3.0-pr-41013-8".;

Daniel Rosenwasser (@DanielRosenwasser)
The results of the perf run you requested are in!

Here they are:

Comparison Report - master..41013

Metric	master	41013	Delta	Best	Worst
Angular - node (v10.16.3, x64)
Memory used	344,651k (± 0.02%)	344,706k (± 0.03%)	+54k (+ 0.02%)	344,444k	344,928k
Parse Time	1.91s (± 0.55%)	1.90s (± 0.43%)	-0.01s (- 0.52%)	1.89s	1.92s
Bind Time	0.84s (± 0.57%)	0.84s (± 0.57%)	0.00s ( 0.00%)	0.83s	0.85s
Check Time	5.25s (± 0.47%)	5.25s (± 0.31%)	+0.00s (+ 0.06%)	5.23s	5.29s
Emit Time	5.89s (± 0.38%)	5.91s (± 1.20%)	+0.02s (+ 0.36%)	5.80s	6.16s
Total Time	13.89s (± 0.29%)	13.91s (± 0.58%)	+0.02s (+ 0.12%)	13.78s	14.15s
Compiler-Unions - node (v10.16.3, x64)
Memory used	200,759k (± 0.03%)	200,821k (± 0.03%)	+62k (+ 0.03%)	200,671k	200,923k
Parse Time	0.79s (± 0.51%)	0.78s (± 0.97%)	-0.01s (- 0.63%)	0.77s	0.80s
Bind Time	0.53s (± 1.27%)	0.52s (± 0.91%)	-0.00s (- 0.76%)	0.51s	0.53s
Check Time	7.59s (± 0.57%)	7.59s (± 0.65%)	-0.00s (- 0.05%)	7.47s	7.72s
Emit Time	2.51s (± 1.43%)	2.48s (± 0.90%)	-0.03s (- 1.12%)	2.43s	2.52s
Total Time	11.42s (± 0.47%)	11.38s (± 0.53%)	-0.04s (- 0.36%)	11.24s	11.56s
Monaco - node (v10.16.3, x64)
Memory used	341,715k (± 0.01%)	341,688k (± 0.02%)	-27k (- 0.01%)	341,565k	341,920k
Parse Time	1.56s (± 0.50%)	1.57s (± 0.61%)	+0.01s (+ 0.38%)	1.54s	1.59s
Bind Time	0.74s (± 0.78%)	0.74s (± 0.98%)	-0.00s (- 0.13%)	0.73s	0.76s
Check Time	5.38s (± 0.34%)	5.38s (± 0.52%)	-0.00s (- 0.02%)	5.31s	5.45s
Emit Time	3.02s (± 0.86%)	3.01s (± 0.75%)	-0.01s (- 0.20%)	2.97s	3.06s
Total Time	10.70s (± 0.39%)	10.70s (± 0.45%)	-0.00s (- 0.05%)	10.59s	10.80s
TFS - node (v10.16.3, x64)
Memory used	304,178k (± 0.03%)	304,226k (± 0.02%)	+48k (+ 0.02%)	304,099k	304,366k
Parse Time	1.22s (± 0.55%)	1.21s (± 0.48%)	-0.00s (- 0.33%)	1.20s	1.23s
Bind Time	0.71s (± 0.78%)	0.71s (± 1.03%)	-0.00s (- 0.56%)	0.69s	0.72s
Check Time	4.79s (± 0.42%)	4.80s (± 0.47%)	+0.01s (+ 0.23%)	4.73s	4.84s
Emit Time	3.21s (± 1.33%)	3.18s (± 1.60%)	-0.03s (- 1.00%)	3.03s	3.27s
Total Time	9.93s (± 0.53%)	9.90s (± 0.66%)	-0.02s (- 0.24%)	9.76s	10.03s
material-ui - node (v10.16.3, x64)
Memory used	474,572k (± 0.02%)	474,591k (± 0.01%)	+19k (+ 0.00%)	474,488k	474,712k
Parse Time	1.94s (± 0.79%)	1.94s (± 0.41%)	-0.00s (- 0.10%)	1.92s	1.96s
Bind Time	0.65s (± 1.23%)	0.65s (± 0.80%)	-0.00s (- 0.15%)	0.64s	0.66s
Check Time	14.81s (± 0.66%)	14.76s (± 0.64%)	-0.06s (- 0.39%)	14.63s	15.10s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	17.41s (± 0.63%)	17.35s (± 0.54%)	-0.06s (- 0.35%)	17.24s	17.70s
Angular - node (v12.1.0, x64)
Memory used	322,324k (± 0.02%)	322,310k (± 0.02%)	-14k (- 0.00%)	322,163k	322,427k
Parse Time	1.91s (± 0.63%)	1.91s (± 0.66%)	-0.00s (- 0.05%)	1.88s	1.94s
Bind Time	0.82s (± 0.73%)	0.82s (± 0.70%)	-0.00s (- 0.61%)	0.81s	0.84s
Check Time	5.17s (± 0.48%)	5.14s (± 0.42%)	-0.03s (- 0.52%)	5.11s	5.21s
Emit Time	6.16s (± 0.82%)	6.15s (± 0.87%)	-0.02s (- 0.24%)	6.06s	6.27s
Total Time	14.07s (± 0.49%)	14.02s (± 0.46%)	-0.05s (- 0.35%)	13.91s	14.21s
Compiler-Unions - node (v12.1.0, x64)
Memory used	187,812k (± 0.14%)	188,033k (± 0.15%)	+221k (+ 0.12%)	187,234k	188,396k
Parse Time	0.77s (± 0.62%)	0.77s (± 0.84%)	-0.01s (- 0.65%)	0.76s	0.78s
Bind Time	0.53s (± 0.89%)	0.53s (± 0.98%)	-0.00s (- 0.19%)	0.52s	0.54s
Check Time	7.04s (± 0.64%)	7.02s (± 0.42%)	-0.02s (- 0.30%)	6.98s	7.10s
Emit Time	2.49s (± 1.00%)	2.47s (± 1.28%)	-0.02s (- 1.00%)	2.43s	2.57s
Total Time	10.84s (± 0.63%)	10.79s (± 0.32%)	-0.05s (- 0.49%)	10.69s	10.85s
Monaco - node (v12.1.0, x64)
Memory used	324,057k (± 0.02%)	324,057k (± 0.01%)	+0k (+ 0.00%)	323,992k	324,106k
Parse Time	1.54s (± 0.71%)	1.54s (± 0.87%)	+0.00s (+ 0.19%)	1.52s	1.58s
Bind Time	0.72s (± 1.20%)	0.72s (± 0.62%)	-0.00s (- 0.55%)	0.71s	0.73s
Check Time	5.20s (± 0.29%)	5.21s (± 0.63%)	+0.01s (+ 0.23%)	5.13s	5.28s
Emit Time	3.06s (± 0.70%)	3.06s (± 1.26%)	-0.00s (- 0.03%)	3.02s	3.21s
Total Time	10.52s (± 0.33%)	10.54s (± 0.60%)	+0.01s (+ 0.12%)	10.41s	10.72s
TFS - node (v12.1.0, x64)
Memory used	288,711k (± 0.01%)	288,704k (± 0.01%)	-7k (- 0.00%)	288,622k	288,776k
Parse Time	1.21s (± 0.78%)	1.21s (± 0.43%)	-0.00s (- 0.16%)	1.20s	1.22s
Bind Time	0.70s (± 1.16%)	0.69s (± 0.86%)	-0.01s (- 1.14%)	0.68s	0.71s
Check Time	4.70s (± 0.61%)	4.70s (± 0.45%)	-0.00s (- 0.04%)	4.66s	4.75s
Emit Time	3.18s (± 1.55%)	3.17s (± 0.46%)	-0.01s (- 0.35%)	3.14s	3.21s
Total Time	9.80s (± 0.64%)	9.78s (± 0.24%)	-0.02s (- 0.22%)	9.73s	9.83s
material-ui - node (v12.1.0, x64)
Memory used	452,433k (± 0.05%)	452,478k (± 0.01%)	+45k (+ 0.01%)	452,351k	452,672k
Parse Time	1.94s (± 0.38%)	1.95s (± 0.37%)	+0.01s (+ 0.52%)	1.93s	1.96s
Bind Time	0.64s (± 0.63%)	0.64s (± 1.17%)	-0.00s (- 0.31%)	0.63s	0.66s
Check Time	13.30s (± 0.52%)	13.26s (± 0.40%)	-0.04s (- 0.32%)	13.15s	13.41s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	15.88s (± 0.43%)	15.84s (± 0.36%)	-0.04s (- 0.23%)	15.73s	15.99s
Angular - node (v14.15.1, x64)
Memory used	321,052k (± 0.01%)	321,051k (± 0.00%)	-2k (- 0.00%)	321,024k	321,066k
Parse Time	1.90s (± 0.66%)	1.90s (± 0.53%)	+0.00s (+ 0.11%)	1.89s	1.93s
Bind Time	0.87s (± 0.66%)	0.87s (± 0.51%)	+0.00s (+ 0.23%)	0.86s	0.88s
Check Time	5.15s (± 0.44%)	5.16s (± 0.46%)	+0.00s (+ 0.08%)	5.08s	5.20s
Emit Time	6.19s (± 0.64%)	6.22s (± 0.75%)	+0.03s (+ 0.52%)	6.10s	6.33s
Total Time	14.11s (± 0.28%)	14.15s (± 0.45%)	+0.04s (+ 0.29%)	14.02s	14.31s
Compiler-Unions - node (v14.15.1, x64)
Memory used	188,505k (± 0.64%)	188,815k (± 0.62%)	+310k (+ 0.16%)	186,850k	190,136k
Parse Time	0.80s (± 0.59%)	0.80s (± 0.56%)	+0.00s (+ 0.25%)	0.79s	0.81s
Bind Time	0.55s (± 0.62%)	0.55s (± 0.62%)	0.00s ( 0.00%)	0.55s	0.56s
Check Time	7.13s (± 0.47%)	7.16s (± 0.72%)	+0.03s (+ 0.36%)	7.09s	7.29s
Emit Time	2.49s (± 0.83%)	2.48s (± 0.63%)	-0.01s (- 0.44%)	2.45s	2.52s
Total Time	10.98s (± 0.36%)	10.99s (± 0.49%)	+0.01s (+ 0.11%)	10.92s	11.14s
Monaco - node (v14.15.1, x64)
Memory used	323,144k (± 0.01%)	323,129k (± 0.01%)	-15k (- 0.00%)	323,075k	323,158k
Parse Time	1.57s (± 0.70%)	1.57s (± 0.64%)	+0.01s (+ 0.38%)	1.55s	1.60s
Bind Time	0.75s (± 0.77%)	0.75s (± 0.60%)	-0.00s (- 0.27%)	0.74s	0.76s
Check Time	5.19s (± 0.30%)	5.17s (± 0.45%)	-0.01s (- 0.19%)	5.14s	5.24s
Emit Time	3.13s (± 0.67%)	3.11s (± 0.68%)	-0.02s (- 0.61%)	3.08s	3.17s
Total Time	10.63s (± 0.23%)	10.61s (± 0.38%)	-0.02s (- 0.23%)	10.54s	10.74s
TFS - node (v14.15.1, x64)
Memory used	287,663k (± 0.01%)	287,670k (± 0.01%)	+7k (+ 0.00%)	287,626k	287,720k
Parse Time	1.27s (± 1.48%)	1.27s (± 1.21%)	-0.00s (- 0.08%)	1.23s	1.30s
Bind Time	0.72s (± 1.17%)	0.72s (± 0.81%)	-0.00s (- 0.55%)	0.71s	0.73s
Check Time	4.70s (± 0.38%)	4.73s (± 0.45%)	+0.03s (+ 0.55%)	4.67s	4.77s
Emit Time	3.26s (± 0.40%)	3.29s (± 0.83%)	+0.03s (+ 0.80%)	3.23s	3.38s
Total Time	9.95s (± 0.27%)	10.00s (± 0.47%)	+0.05s (+ 0.48%)	9.92s	10.11s
material-ui - node (v14.15.1, x64)
Memory used	450,697k (± 0.00%)	450,711k (± 0.01%)	+14k (+ 0.00%)	450,646k	450,831k
Parse Time	2.00s (± 0.62%)	1.98s (± 1.10%)	-0.02s (- 0.80%)	1.93s	2.03s
Bind Time	0.70s (± 0.74%)	0.70s (± 0.85%)	-0.00s (- 0.43%)	0.69s	0.71s
Check Time	13.61s (± 0.91%)	13.41s (± 0.66%)	-0.20s (- 1.48%)	13.16s	13.55s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	16.31s (± 0.76%)	16.09s (± 0.65%)	-0.22s (- 1.32%)	15.78s	16.28s

System

Machine Name	ts-ci-ubuntu
Platform	linux 4.4.0-206-generic
Architecture	x64
Available Memory	16 GB
Available Memory	7 GB
CPUs	4 × Intel(R) Core(TM) i7-4770 CPU @ 3.40GHz

Hosts

node (v10.16.3, x64)
node (v12.1.0, x64)
node (v14.15.1, x64)

Scenarios

Angular - node (v10.16.3, x64)
Angular - node (v12.1.0, x64)
Angular - node (v14.15.1, x64)
Compiler-Unions - node (v10.16.3, x64)
Compiler-Unions - node (v12.1.0, x64)
Compiler-Unions - node (v14.15.1, x64)
Monaco - node (v10.16.3, x64)
Monaco - node (v12.1.0, x64)
Monaco - node (v14.15.1, x64)
TFS - node (v10.16.3, x64)
TFS - node (v12.1.0, x64)
TFS - node (v14.15.1, x64)
material-ui - node (v10.16.3, x64)
material-ui - node (v12.1.0, x64)
material-ui - node (v14.15.1, x64)

Benchmark	Name	Iterations
Current	41013	10
Baseline	master	10

Developer Information:

Download Benchmark

commandLineParser entry should make the new flag a strict one, I think.

except for this, I'm not convinced we even need a new test, since we know that unknown narrows, and from some other tests, that strict changes the type of the catch variable to unknown.

I guess there's nothing to change here, except possibly dropping the narrowing tests from this test.

I added that style of code in because most of the purpose of this feature is to ensure that catch variables are narrowed, and that we error on usages if a user doesn't do so.

Meta: I was confused by the initial comment, because I wasn't familiar with unknown. I'd say that the first snippet, with catch (err) should not have a comment indicating the error (because IIUC without the new flag it doesn't produce an error), and the second snippet, with explicit catch (err: unknown) should have the error comment, because even without the new flag that's an error. (Right?)

Guido van Rossum (@gvanrossum) good call, thanks! Must have been an earlier copy/paste error.

👍🏼 Does what we talked about in the design meeting.

Side note: It's a little worrying that we don't already have more tests with both (1) catch and (2) strict: true.

Fixes the `no-throw-literal` rule configuration for TypeScript by enabling the appropriate rule in the TypeScript config, per [documentation](https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/no-throw-literal.md#how-to-use). This is timely due to recent [changes to TypeScript](microsoft/TypeScript#41013).

Typescript 4.x changes the default behaviour of try catch and its err type from `any` to [`unknown`](microsoft/TypeScript#41013). This change ensures that where we rely on said variable it is cast accordingly as an `Error`.

* build(deps): update dependency typescript to v4.4.2 * fix(web): cast try catch err type to error Typescript 4.x changes the default behaviour of try catch and its err type from `any` to [`unknown`](microsoft/TypeScript#41013). This change ensures that where we rely on said variable it is cast accordingly as an `Error`. Co-authored-by: Renovate Bot <bot@renovateapp.com> Co-authored-by: Amir Zarrinkafsh <nightah@me.com>

Is there a way to type a function that it throws specific types? So that catch could know what to expect.

Like a func that can throw MyError, and then catch knows that e is MyError.

Should the flag useUnknownInCatchVariables also affect the return type of Promise.prototype.catch?

https://www.typescriptlang.org/play?strict=false&useUnknownInCatchVariables=true#code/C4JwngBA3gsAUBCB6JEB0H4F8IGMCGwuAFhABQCmIIAlNPIihAOoUTH4BubwA9hNxABLAGaQqICEIDOEfADsGyVBN6SARhRFq2AV2lD5AcynA5s3vIpolo8hKnzpwBbgq8REAKLU1dWAiIeJbSvAA21mG8RpTUaAC2FNLS+EYUNADcSljY8PAiFETEZADkJTRoBEVksSB+EAC8AHz0gUzEVGyqkjIQHhDAYAAObApg2DRAA

Should the flag useUnknownInCatchVariables also affect the return type of Promise.prototype.catch?

Guilherme Simoes (@guilhermesimoes) #45602 proposes that idea.

TypeScript Bot (typescript-bot) added the For Uncommitted Bug PR for untriaged, rejected, closed or missing bug label Oct 9, 2020

Daniel Rosenwasser (DanielRosenwasser) changed the title 'unknown' in catch variables --useUnknownInCatchVariables Oct 9, 2020

Daniel Rosenwasser (DanielRosenwasser) changed the title --useUnknownInCatchVariables Add flag to change 'catch' variable default to 'unknown' Oct 9, 2020

Daniel Rosenwasser (DanielRosenwasser) force-pushed the unknownInCatchVariables branch from 87b36c9 to bbb3bfb Compare October 9, 2020 21:08

Daniel Rosenwasser (DanielRosenwasser) marked this pull request as ready for review October 9, 2020 21:10

Nathan Shively-Sanders (sandersn) added the Experiment A fork with an experimental idea which might not make it into master label Oct 20, 2020

Daniel Rosenwasser (DanielRosenwasser) force-pushed the unknownInCatchVariables branch from bbb3bfb to cccf22a Compare December 2, 2020 21:19

This was referenced Dec 4, 2020

Design Meeting Notes, 12/4/2020 #41824

Closed

Design Meeting Notes, 12/9/2020 #41907

Closed

Daniel Rosenwasser (DanielRosenwasser) closed this Feb 9, 2021

Daniel Rosenwasser (DanielRosenwasser) reopened this Feb 9, 2021

Daniel Rosenwasser (DanielRosenwasser) and others added 6 commits May 5, 2021 21:27

Add test case for 'useUnknownInCatchVariables'.

ac4490c

Add new 'useUnknownInCatchVariables' flag.

07a9e49

Accepted baselines.

4f0baa0

Add test for catch variable explicitly typed as 'any'.

cc6e761

Accepted baselines.

cd08b62

Move option under 'strict'.

f529457

Daniel Rosenwasser (DanielRosenwasser) force-pushed the unknownInCatchVariables branch from 7c01840 to f529457 Compare May 5, 2021 21:36

Accepted baselines.

a32013b

Daniel Rosenwasser (DanielRosenwasser) removed the Experiment A fork with an experimental idea which might not make it into master label May 5, 2021

TypeScript Bot (typescript-bot) added the For Milestone Bug PRs that fix a bug with a specific milestone label May 14, 2021

Daniel Rosenwasser (DanielRosenwasser) requested a review from Anders Hejlsberg (ahejlsberg) May 14, 2021 19:11

Nathan Shively-Sanders (sandersn) requested changes May 18, 2021

View reviewed changes

'useUnknownInCatchVariables' is strict in command line help.

0ea20ff

Daniel Rosenwasser (DanielRosenwasser) requested a review from Nathan Shively-Sanders (sandersn) June 1, 2021 21:45

Nathan Shively-Sanders (sandersn) approved these changes Jun 2, 2021

View reviewed changes

Merge remote-tracking branch 'origin/main' into unknownInCatchVariables

49e652d

Daniel Rosenwasser (DanielRosenwasser) merged commit 9906092 into main Jun 3, 2021

Daniel Rosenwasser (DanielRosenwasser) deleted the unknownInCatchVariables branch June 3, 2021 20:13

Daniel Rosenwasser (DanielRosenwasser) added the Breaking Change Would introduce errors in existing code label Jun 3, 2021

Kubilay Kahveci (mkubilayk) mentioned this pull request Jul 20, 2021

Bloomberg feedback on TypeScript 4.4 Beta #45117

Closed

Jack Works (Jack-Works) mentioned this pull request Aug 2, 2021

chore: improve eslint DimensionDev/Maskbook#3835

Merged

Erik Marks (rekmarks) mentioned this pull request Aug 28, 2021

Fix no-throw-literal config for TypeScript MetaMask/eslint-config#201

Merged

Jani Kraner (kr8n3r) mentioned this pull request Aug 31, 2021

Upgrade typescript and fix unknown ypes govuk-paas/paas-admin#1787

Merged

Kukhyeon Heo (sainthkh) mentioned this pull request Nov 16, 2021

chore: Update TypeScript to 4.4.4 cypress-io/cypress#18930

Merged

This was referenced Dec 6, 2021

docs(eslint-plugin): Mention useUnknownInCatchVariables in no-implicit-any-catch typescript-eslint/typescript-eslint#4252

Merged

useUnknownInCatchVariables does not apply to Promise#catch() #47033

Closed

wbt mentioned this pull request Dec 17, 2021

Error in catch clause should be unknown #26174

Closed

4 tasks

Sam Goldman (samwgoldman) mentioned this pull request Mar 9, 2022

catch clause annotations tc39/proposal-type-annotations#47

Open

Michael Molisani (molisani) mentioned this pull request Jul 11, 2022

Infer instance type arguments as constraint #49863

Closed

ndaemy (ndaemy) mentioned this pull request May 8, 2024

[Refactor]Complete mju-likelion/custard-pudding#110

Merged

Microsoft (microsoft) locked as resolved and limited conversation to collaborators Oct 21, 2025

		@@ -0,0 +1,35 @@
		// @useUnknownInCatchVariables: true

Add flag to change `catch` variables' default types to `unknown` by DanielRosenwasser · Pull Request #41013 · microsoft/TypeScript · GitHub

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Add flag to change catch variables' default types to unknown - #41013

Add flag to change catch variables' default types to unknown#41013Daniel Rosenwasser (DanielRosenwasser) merged 9 commits intomainmicrosoft/TypeScript:mainfrom unknownInCatchVariablesmicrosoft/TypeScript:unknownInCatchVariablesCopy head branch name to clipboard

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Add flag to change catch variables' default types to unknown#41013
Daniel Rosenwasser (DanielRosenwasser) merged 9 commits into
mainfrom
unknownInCatchVariables

Daniel Rosenwasser (DanielRosenwasser) commented Oct 9, 2020 •
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