microsoft/TypeScript · error · Error

tsserverlibrary requires CommonJS; use typescript.js instead

Error message

tsserverlibrary requires CommonJS; use typescript.js instead

What it means

The TypeScript build generates a tsserverlibrary.js shim that only works under CommonJS: it checks `typeof module !== "undefined" && module.exports` and otherwise throws. tsserverlibrary is intentionally Node/CommonJS-only (it re-exports ./typescript.js); the wrapper blocks ESM and browser loads because the full compiler bundle is neither ESM-safe nor browser-safe.

Source

Thrown at Herebyfile.mjs:487

    description: "Builds only tsc and tsserver",
    dependencies: [tsc, tsserver],
});

export const watchMin = task({
    name: "watch-min",
    description: "Watches only tsc and tsserver",
    hiddenFromTaskList: true,
    dependencies: [watchTsc, watchTsserver],
});

// This is technically not enough to make tsserverlibrary loadable in the
// browser, but it's unlikely that anyone has actually been doing that.
const lsslJs = `
if (typeof module !== "undefined" && module.exports) {
    module.exports = require("./typescript.js");
}
else {
    throw new Error("tsserverlibrary requires CommonJS; use typescript.js instead");
}
`;

const lsslDts = `
import ts = require("./typescript.js");
export = ts;
`;

const lsslDtsInternal = `
import ts = require("./typescript.internal.js");
export = ts;
`;

/**
 * @param {string} contents
 */
async function fileContentsWithCopyright(contents) {
    return await getCopyrightHeader() + contents.trim().replace(/\r\n/g, "\n") + "\n";

View on GitHub (pinned to b465fdbfe1)

Solutions

1. Import 'typescript.js' instead of 'tsserverlibrary.js' (or use the package root 'typescript') in ESM/browser code.
2. If you need tsserverlibrary specifically, load it via `require()` under CommonJS, or configure your bundler to treat it as CJS (module.type === 'commonjs').
3. For browser-based language-service work, use a browser-packaged build rather than tsserverlibrary.

Example fix

// before
import ts from "./tsserverlibrary.js"; // throws in ESM/browser

// after
import ts from "./typescript.js";
// or, under CommonJS:
const ts = require("./tsserverlibrary.js");

// Verify the module system before importing tsserverlibrary.
const isCommonJS = typeof module !== "undefined" && !!module.exports;
if (!isCommonJS) {
  throw new Error("Load typescript.js instead of tsserverlibrary.js under ESM/browser.");
}
const ts = require("./tsserverlibrary.js");

When it happens

Trigger: Importing the built 'built/local/tsserverlibrary.js' (or the published 'tsserverlibrary.js') via an ES module `import`, through a bundler emitting ESM, or in a browser where the global `module` object is undefined.

Common situations: Editor plugins or tooling that static-import tsserverlibrary; Webpack/Rollup configs with `output.module: true` or `type: "module"`; consuming the published package from a `.mjs` file.

Related errors

• LKG cannot be created when --bundle=false
• Cannot replace the LKG unless all built targets are present
• Diagnostic code ${code} appears more than once.
• Expected ${inputDir} to be a directory
• Expected ${inputFile} to be a file

AI-assisted analysis of microsoft/TypeScript@b465fdbfe1 (2026-08-12). Data as JSON: /api/errors/cd0d505502d0dfa3. Report an issue: GitHub.