How do I import an ES6 JavaScript module in my VS Code extension written in TypeScript?

Question

I am developing a VS Code extension in TypeScript and I am trying to import a JavaScript library from npm that is packaged with "type": "module", in its package.json.

If I simply do import * as mylib from mylib I get this error message:

Activating extension 'undefined_publisher.curlconverter' failed: Must use import to load ES Module: /Users/space/code/curlconverter-extension/curlconverter/node_modules/curlconverter/index.js require() of ES modules is not supported. require() of /Users/space/code/curlconverter-extension/curlconverter/node_modules/curlconverter/index.js from /Users/space/code/curlconverter-extension/curlconverter/out/extension.js is an ES module file as it is a .js file whose nearest parent package.json contains "type": "module" which defines all .js files in that package scope as ES modules. Instead rename index.js to end in .cjs, change the requiring code to use import(), or remove "type": "module" from /Users/space/code/curlconverter-extension/curlconverter/node_modules/curlconverter/package.json. .

This is telling me that the generated JS from TS in out/extension.js is using a require() statement to try and load that ES6 module and that obviously fails.

I tried to get it to generate code that uses import instead by adding this line to my tsconfig.json

        "module": "ES2020",

but then I get this error message (even if I comment out the import statement of that library, so my extension becomes just something that registers a command that does nothing) when I run my extension's command:

Activating extension 'undefined_publisher.curlconverter' failed: Cannot use import statement outside a module.

Do I need to add a package.json with "type": "module", to out/ or something?

Answer 1

Yes, this is a pain. To be specific, you can develop and debug extensions using es6 modules in vscode, but you cannot deploy them. You get the error message (as late) as when you execute your vsix package.

And ist doesn't look likeley to change any time soon: https://github.com/electron/electron/issues/21457

However, we do not want to code in commonjs modules any longer. Good news - there is a both pleasant enough and automisable workaround, as we found:

1. Code in es6 using only dynamic imports from your root plugin file. For dynamic imports are both valid in es6 and commonjs. (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/import#dynamic_imports)
2. debug against es6 modules as you would expect (using F5) .
3. deploy with transpiling your es6 modules to cjs quickly to es6, using for instance the typescript-compiler like so: npx tsc -p tsconfig.json

using a tsconfing.json like

{
    "exclude": [ "node_modules", "cjs" ],
  "compilerOptions": {
    /* Visit https://aka.ms/tsconfisg.json to read more about this file */

    /* Basic Options */
    // "incremental": true,                         /* Enable incremental compilation */
    "target": "esnext",                                /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', 'ES2018', 'ES2019', 'ES2020', 'ES2021', or 'ESNEXT'. */
    "module": "commonjs",                           /* Specify module code generation: 'none', 'commonjs', 'amd', 'system', 'umd', 'es2015', 'es2020', or 'ESNext'. */
    /// "lib": [ "ESNext"],                                   /* Specify library files to be included in the compilation. */
    "allowJs": true,                             /* Allow javascript files to be compiled. */
    "checkJs": false,                             /* Report errors in .js files. */
    // "jsx": "preserve",                           /* Specify JSX code generation: 'preserve', 'react-native', 'react', 'react-jsx' or 'react-jsxdev'. */
    // "declaration": true,                         /* Generates corresponding '.d.ts' file. */
    // "declarationMap": true,                      /* Generates a sourcemap for each corresponding '.d.ts' file. */
    // "sourceMap": true,                           /* Generates corresponding '.map' file. */
    // "outFile": "./",                             /* Concatenate and emit output to single file. */
    "outDir": "./cjs",                              /* Redirect output structure to the directory. */
    // "rootDir": "./",                             /* Specify the root directory of input files. Use to control the output directory structure with --outDir. */
    // "composite": true,                           /* Enable project compilation */
    // "tsBuildInfoFile": "./",                     /* Specify file to store incremental compilation information */
    // "removeComments": true,                      /* Do not emit comments to output. */
    // "noEmit": true,                              /* Do not emit outputs. */
    // "importHelpers": true,                       /* Import emit helpers from 'tslib'. */
    "downlevelIteration": true,                  /* Provide full support for iterables in 'for-of', spread, and destructuring when targeting 'ES5' or 'ES3'. */
    // "isolatedModules": true,                     /* Transpile each file as a separate module (similar to 'ts.transpileModule'). */

    /* Strict Type-Checking Options */
    // "strict": true,                                 /* Enable all strict type-checking options. */
    // "noImplicitAny": true,                       /* Raise error on expressions and declarations with an implied 'any' type. */
    // "strictNullChecks": true,                    /* Enable strict null checks. */
    // "strictFunctionTypes": true,                 /* Enable strict checking of function types. */
    // "strictBindCallApply": true,                 /* Enable strict 'bind', 'call', and 'apply' methods on functions. */
    // "strictPropertyInitialization": true,        /* Enable strict checking of property initialization in classes. */
    // "noImplicitThis": true,                      /* Raise error on 'this' expressions with an implied 'any' type. */
    // "alwaysStrict": true,                        /* Parse in strict mode and emit "use strict" for each source file. */

    /* Additional Checks */
    // "noUnusedLocals": true,                      /* Report errors on unused locals. */
    // "noUnusedParameters": true,                  /* Report errors on unused parameters. */
    // "noImplicitReturns": true,                   /* Report error when not all code paths in function return a value. */
    // "noFallthroughCasesInSwitch": true,          /* Report errors for fallthrough cases in switch statement. */
    // "noUncheckedIndexedAccess": true,            /* Include 'undefined' in index signature results */
    // "noImplicitOverride": true,                  /* Ensure overriding members in derived classes are marked with an 'override' modifier. */
    // "noPropertyAccessFromIndexSignature": true,  /* Require undeclared properties from index signatures to use element accesses. */

    /* Module Resolution Options */
    "moduleResolution": "node",                  /* Specify module resolution strategy: 'node' (Node.js) or 'classic' (TypeScript pre-1.6). */
    // "baseUrl": "./",                             /* Base directory to resolve non-absolute module names. */
    // "paths": {},                                 /* A series of entries which re-map imports to lookup locations relative to the 'baseUrl'. */
    // "rootDirs": [],                              /* List of root folders whose combined content represents the structure of the project at runtime. */
    // "typeRoots": [],                             /* List of folders to include type definitions from. */
    // "types": [],                                 /* Type declaration files to be included in compilation. */
    // "allowSyntheticDefaultImports": true,        /* Allow default imports from modules with no default export. This does not affect code emit, just typechecking. */
    "esModuleInterop": true,                        /* Enables emit interoperability between CommonJS and ES Modules via creation of namespace objects for all imports. Implies 'allowSyntheticDefaultImports'. */
    // "preserveSymlinks": true,                    /* Do not resolve the real path of symlinks. */
    // "allowUmdGlobalAccess": true,                /* Allow accessing UMD globals from modules. */

    /* Source Map Options */
    // "sourceRoot": "",                            /* Specify the location where debugger should locate TypeScript files instead of source locations. */
    // "mapRoot": "",                               /* Specify the location where debugger should locate map files instead of generated locations. */
    // "inlineSourceMap": true,                     /* Emit a single file with source maps instead of having a separate file. */
    // "inlineSources": true,                       /* Emit the source alongside the sourcemaps within a single file; requires '--inlineSourceMap' or '--sourceMap' to be set. */

    /* Experimental Options */
    // "experimentalDecorators": true,              /* Enables experimental support for ES7 decorators. */
    // "emitDecoratorMetadata": true,               /* Enables experimental support for emitting type metadata for decorators. */

    /* Advanced Options */
    "skipLibCheck": true,                           /* Skip type checking of declaration files. */
    "forceConsistentCasingInFileNames": true        /* Disallow inconsistently-cased references to the same file. */
  }
}

Answer 2

You can't. VS Code is an Electron app and Electron apps can't use ES6 modules (yet).

https://github.com/electron/electron/issues/21457