swc transpiler does not set `strictMode` to match tsconfig #1531

Janpot · 2021-10-26T13:54:54Z

Search Terms

swc

Expected Behavior

Running

function defaultHello () {
  return ''
}

class X {
  constructor(x) {
    this.hello = () => (x.hello || defaultHello)()
  }
}

console.log(new X({
  hello () {
    return this.y || 'this works'
  }
}).hello())

using

  "ts-node": {
    "transpileOnly": true,
    "transpiler": "ts-node/transpilers/swc-experimental"
  },

will print

this works

(this is what is printed without using swc)

Actual Behavior

an error is printed:

/swctest/index.ts:13
    return this.y || 'this works'
                ^
TypeError: Cannot read property 'y' of undefined
    at hello (/swctest/index.ts:13:17)
    at X.hello (/swctest/index.ts:7:50)
    at Object.<anonymous> (/swctest/index.ts:15:4)
    at Module._compile (internal/modules/cjs/loader.js:1063:30)
    at Module.m._compile (/swctest/node_modules/ts-node/src/index.ts:1371:23)
    at Module._extensions..js (internal/modules/cjs/loader.js:1092:10)
    at Object.require.extensions.<computed> [as .ts] (/swctest/node_modules/ts-node/src/index.ts:1374:12)
    at Module.load (internal/modules/cjs/loader.js:928:32)
    at Function.Module._load (internal/modules/cjs/loader.js:769:14)
    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:72:12)

Specifications

ts-node v10.4.0
node v14.16.0
compiler v4.4.4
@swc/core 1.2.103

tsconfig.json, if you're using one:

{
  "compilerOptions": {
    "target": "es5",                 
    "module": "commonjs",
    "esModuleInterop": true, 
    "forceConsistentCasingInFileNames": true, 
    "strict": false,  
    "skipLibCheck": true },

  "ts-node": {
    "transpileOnly": true,
    "transpiler": "ts-node/transpilers/swc-experimental"
  },
}

Operating system and version: MacOS 11.6

The text was updated successfully, but these errors were encountered:

cspotcode · 2021-10-26T17:59:53Z

Do you think this is a strict mode issue? E.g swc is enabling strict mode when you expect it to be disabled, or vice versa? I'm referring specifically to https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Strict_mode, not to TypeScripts's "strict" option which is a different thing.

What does this do?

console.log(new X({
  hello () {
    console.dir(this); // figure out the `this` value.  Is it equal to `global`?
  }
}).hello())

Janpot · 2021-10-27T07:45:16Z

Ah ofcourse, yes indeed, it's the global object, swc seems to add the use strict pragma. Manually adding it makes the behavior the same when I disable swc.
Aside, I've been trying to use the --emit flag to inspect the transpiler output, but it doesn't seem to have any effect. Am I misunderstanding the purpose of this flag?

cspotcode · 2021-10-27T14:53:15Z

Ok, looks we do not pass the strictMode flag to swc and it defaults to true.
https://swc.rs/docs/config-js-module#strictmode

ts-node/src/transpilers/swc.ts

Lines 85 to 90 in bc03a3e

    
           module: moduleType 
        
             ? ({ 
        
                 noInterop: !esModuleInterop, 
        
                 type: moduleType, 
        
               } as swcTypes.ModuleConfig) 
        
             : undefined,

We should be explicitly setting this option to match whatever your typescript config indicates, so that you'll get the same behavior with both compilers.
https://www.typescriptlang.org/tsconfig#alwaysStrict

I've renamed this issue to describe the underlying problem, which helps keep track of implementing a fix.

Re the --emit flag, it is meant to write all compiled output into a .ts-node directory. But it's possibly non-functional when combined with transpilers / transpile-only? I'm not sure.

I also have this idea to add a flag that is specifically for inspecting the compiled output of a single file at a time, for debugging situations like this: #1366

Janpot · 2021-10-27T15:07:39Z

Re the --emit flag, it is meant to write all compiled output into a .ts-node directory. But it's possibly non-functional when combined with transpilers / transpile-only? I'm not sure.

It never seems to emit for me, regardless of the options

I also have this idea to add a flag that is specifically for inspecting the compiled output of a single file at a time, for debugging situations like this: #1366

Personally, I think I'd still use just --emit

cspotcode · 2021-10-27T15:33:35Z

If you think --emit is not working correctly, feel free to submit a bug report. Please check for pre-existing reports first.

cspotcode · 2021-11-03T02:57:32Z

@Janpot What is your tsconfig? There are various options which affect "use strict" and I want to make sure I understand your project configuration 100%. Thank you in advance.

I did a bit of research here. tsc, by default, will add "use strict" whenever you use any sort of import or export. Additionally, if strict: true is configured, it will always emit "use strict".

Your script above is a special case. I expect that most node scripts, even standalone ones, will have at least one import, for example import {} from 'fs'; TS is bending over backwards to allow scripts with zero imports or exports to run in non-strict mode. I suspect this behavior only exists for backwards compatibility, and you generally always want "use strict" enabled when working with node.

swc is not as nuanced as TS. We can either tell it to always emit use strict, or never emit.

Given this limitation of swc, I'm going to pragmatically assume that all node scripts have an import or export, and set swc's options accordingly.

If a user really really needs to avoid strict mode, they will likely have alwaysStrict: false, noImplicitUseStrict: true. We can detect this and tell swc not to emit "use strict"

cspotcode · 2021-11-03T03:09:47Z

Nevermind... of course you included your tsconfig at the top, doh!

Janpot · 2021-11-03T08:27:49Z

This was originally discovered in a repo that was transitioning from js to ts. all the imports were require calls. not all files had a 'use strict' pragma. the original js files were not compiled before and after running them through ts-node, this issue came up.

cspotcode · 2021-11-03T21:23:30Z

Thanks, good to understand the context. I think the implementation we settled on is the best we can do, given that swc's configuration is a bit more limited than tsc's.

This PR contains the following updates: | Package | Type | Update | Change | |---|---|---|---| | [ts-node](https://typestrong.org/ts-node) ([source](https://github.com/TypeStrong/ts-node)) | devDependencies | minor | [`10.4.0` -> `10.5.0`](https://renovatebot.com/diffs/npm/ts-node/10.4.0/10.5.0) | --- ### Release Notes <details> <summary>TypeStrong/ts-node</summary> ### [`v10.5.0`](https://github.com/TypeStrong/ts-node/releases/v10.5.0) [Compare Source](TypeStrong/ts-node@v10.4.0...v10.5.0)  Questions about this release? Ask in the official discussion thread: [#1634](TypeStrong/ts-node#1634) **Added** - Eliminate "Emit Skipped" errors ([#693](TypeStrong/ts-node#693), [#1345](TypeStrong/ts-node#1345), [#1629](TypeStrong/ts-node#1629)) - Avoids all "Emit Skipped" errors by performing a fallback `transpileOnly`-style transformation. - Does not affect typechecking. Type errors are still detected and thrown. - Fallback has the same limitations as `isolatedModules`. This will only affect rare cases such as using `const enums` with `preserveConstEnums` disabled. - Fixes [#693](TypeStrong/ts-node#693) - Graduate swc transpiler out of experimental; add `swc: true` convenience option ([docs](https://typestrong.org/ts-node/docs/transpilers)) ([#1487](TypeStrong/ts-node#1487), [#1536](TypeStrong/ts-node#1536), [#1613](TypeStrong/ts-node#1613), [#1627](TypeStrong/ts-node#1627)) - `"swc": true` or `--swc` will use swc for faster execution - This feature is no longer marked "experimental." Thank you to everyone who filed bugs! - swc transpiler attempts to load `@swc/core` or `@swc/wasm` dependencies from your project before falling-back to global installations ([#1613](TypeStrong/ts-node#1613), [#1627](TypeStrong/ts-node#1627)) - global fallback only occurs when using a global installation of ts-node - Add support for TypeScript's `traceResolution` output ([docs](https://www.typescriptlang.org/tsconfig/#traceResolution)) ([#1128](TypeStrong/ts-node#1128), [#1491](TypeStrong/ts-node#1491)) [@TheUnlocked](https://github.com/TheUnlocked) - Support import assertions in ESM loader ([docs](https://nodejs.org/dist/latest-v17.x/docs/api/esm.html#import-assertions)) ([#1557](TypeStrong/ts-node#1557), [#1558](TypeStrong/ts-node#1558), [#1559](TypeStrong/ts-node#1559), [#1573](TypeStrong/ts-node#1573)) [@Pokute](https://github.com/Pokute), [@geigerzaehler](https://github.com/geigerzaehler) - Allows importing JSON files from ESM with the requisite flag ([docs](https://nodejs.org/dist/latest-v17.x/docs/api/esm.html#json-modules)) - `ts-node -vvv` also logs absolute paths to `ts-node` and `typescript`, to make it more obvious when you're accidentally using globally-installed versions ([#1323](TypeStrong/ts-node#1323), [#1620](TypeStrong/ts-node#1620)) - Add swc target "es2022" ([#1535](TypeStrong/ts-node#1535), [#1540](TypeStrong/ts-node#1540)) - When you have target es2022 in tsconfig, will use swc's es2022 target **Changed** - Initialize TypeScript compiler before starting REPL prompt ([#1498](TypeStrong/ts-node#1498)) [@TheUnlocked](https://github.com/TheUnlocked) - Improves responsiveness for first line of REPL input - Use `v8-compile-cache-lib` to load typescript - improves startup time ([#1339](TypeStrong/ts-node#1339), [#1603](TypeStrong/ts-node#1603)) - Support both `--camelCase` and `--hyphen-case` for all CLI flags; update documentation to use `--camelCase` ([#1598](TypeStrong/ts-node#1598), [#1599](TypeStrong/ts-node#1599)) - Not a breaking change; CLI continues to accept both forms - Make `TSError` `diagnosticText` property non-enumerable to prevent it from being logged below the stack ([#1632](TypeStrong/ts-node#1632)) **Fixed** - Fix [#1538](TypeStrong/ts-node#1538): REPL inputs fail to transpile via swc ([#1538](TypeStrong/ts-node#1538), [#1541](TypeStrong/ts-node#1541), [#1602](TypeStrong/ts-node#1602)) - Fix [#1478](TypeStrong/ts-node#1478): REPL erroneously logged `undefined` for all inputs after the first when using swc transpiler ([#1478](TypeStrong/ts-node#1478), [#1580](TypeStrong/ts-node#1580), [#1602](TypeStrong/ts-node#1602)) - Fix [#1389](TypeStrong/ts-node#1389): In `--showConfig` output, emit accurate `moduleTypes` paths resolved relative to the `tsconfig.json` which declared them ([#1389](TypeStrong/ts-node#1389), [#1619](TypeStrong/ts-node#1619)) - Fix: Remove indentation from `ts-node --help` output ([#1597](TypeStrong/ts-node#1597), [#1600](TypeStrong/ts-node#1600)) - Fix [#1425](TypeStrong/ts-node#1425): Merged definitions correctly into `tsconfig.schemastore-schema.json` ([#1425](TypeStrong/ts-node#1425), [#1618](TypeStrong/ts-node#1618)) - Fix: Allow disabling `"use strict"` emit in SWC transpiler ([#1531](TypeStrong/ts-node#1531), [#1537](TypeStrong/ts-node#1537)) - Fix: Add missing `ERR_UNKNOWN_FILE_EXTENSION` constructor; was throwing `ERR_UNKNOWN_FILE_EXTENSION is not a constructor` ([#1562](TypeStrong/ts-node#1562)) [@bluelovers](https://github.com/bluelovers) - Fix [#1565](TypeStrong/ts-node#1565): entrypoint resolution failed on node v12.0.x and v12.1.x ([#1565](TypeStrong/ts-node#1565), [#1566](TypeStrong/ts-node#1566)) [@davidmurdoch](https://github.com/davidmurdoch) #### Docs - Explain `env -S` flag for shebangs ([docs](https://typestrong.org/ts-node/docs/usage#shebang)) ([#1448](TypeStrong/ts-node#1448), [#1545](TypeStrong/ts-node#1545)) [@sheeit](https://github.com/sheeit), [@chee](https://github.com/chee) - Suggest `skipIgnore` when you want to compile files in node_modules ([docs](https://typestrong.org/ts-node/docs/how-it-works)) ([#1553](TypeStrong/ts-node#1553)) [@webstrand](https://github.com/webstrand) - Fix typo in `moduleTypes` on options page ([docs](https://typestrong.org/ts-node/docs/options)) ([#1630](TypeStrong/ts-node#1630), [#1633](TypeStrong/ts-node#1633)) #### Misc - Adds experimental `experimentalResolverFeatures` option, but it does not do anything yet ([#1514](TypeStrong/ts-node#1514), [#1614](TypeStrong/ts-node#1614)) https://github.com/TypeStrong/ts-node/milestone/4 </details> --- ### Configuration 📅 **Schedule**: At any time (no schedule defined). 🚦 **Automerge**: Disabled by config. 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cspotcode changed the title ~~swc transpiler generates faulty behavior~~ swc transpiler does not set strictMode to match tsconfig Oct 27, 2021

cspotcode added this to the next milestone Oct 27, 2021

Janpot mentioned this issue Oct 27, 2021

--emit option is not emitting files #1532

Closed

cspotcode mentioned this issue Nov 3, 2021

allow disabling "use strict" emit in SWC when you reeeally want to #1537

Merged

cspotcode closed this as completed in #1537 Nov 3, 2021

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swc transpiler does not set `strictMode` to match tsconfig #1531

swc transpiler does not set `strictMode` to match tsconfig #1531

Janpot commented Oct 26, 2021 •

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cspotcode commented Nov 3, 2021

swc transpiler does not set strictMode to match tsconfig #1531

swc transpiler does not set strictMode to match tsconfig #1531

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Janpot commented Oct 26, 2021 • edited Loading

Search Terms

Expected Behavior

Actual Behavior

Specifications

cspotcode commented Oct 26, 2021

Janpot commented Oct 27, 2021 • edited Loading

cspotcode commented Oct 27, 2021

Janpot commented Oct 27, 2021 • edited Loading

cspotcode commented Oct 27, 2021

cspotcode commented Nov 3, 2021 • edited Loading

cspotcode commented Nov 3, 2021

Janpot commented Nov 3, 2021

cspotcode commented Nov 3, 2021

swc transpiler does not set `strictMode` to match tsconfig #1531

swc transpiler does not set `strictMode` to match tsconfig #1531

Janpot commented Oct 26, 2021 •

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Janpot commented Oct 27, 2021 •

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Janpot commented Oct 27, 2021 •

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cspotcode commented Nov 3, 2021 •

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