TypeScript Diagnostic Service

Common errors

• TypeError: service.update is not a function

  cause Attempting to use the `update` method, which was removed in version 2.0.0.
  fix The `update` method was removed. Use `getSourceFile` or `getDiagnostics` which accept an optional `sourceText` parameter to provide file content.

• Error: Cannot find module 'typescript-service' or 'require is not defined'

  cause Incorrect module import syntax (e.g., `require` in an ESM context) or the package is not correctly installed/resolved.
  fix Ensure `npm install typescript-service` is run. For module issues, check your project's `type` in `package.json` and `tsconfig.json`'s `module` and `moduleResolution` settings. If your project is ESM, try `import { createService } from 'typescript-service';`. If CJS, try `const { createService } = require('typescript-service');`.

• TS2345: Argument of type 'string | number | boolean' is not assignable to parameter of type 'string'.

  cause Compatibility issues with newer TypeScript versions where `ts.Diagnostic` or other types have changed or become stricter, leading to type mismatches when using the old API.
  fix This often indicates a fundamental incompatibility with your current TypeScript version. You may need to either downgrade your TypeScript version to one closer to the package's last update (e.g., TypeScript 3.x), or switch to an actively maintained library. Manual type assertions (`as any`) might temporarily silence errors but won't resolve underlying runtime issues.

• Error: getSourceFile fail fixed if file is not defined in tsconfig

  cause The `getSourceFile` method failed because the specified file was not included in the `tsconfig.json`'s scope.
  fix Ensure all files you intend to process with `typescript-service` are included in the `files`, `include`, or `references` sections of your `tsconfig.json`. Alternatively, provide the `sourceText` parameter to `getDiagnostics` or `getSourceFile` if the file is outside the configured project scope.

Warnings

• breaking The `update` method was removed in version 2.0.0. Code relying on this method will break.
  Fix: Migrate to using `getSourceFile` with the `sourceText` parameter if you need to provide file content, or simply call `getDiagnostics` which can accept `sourceText`.
• breaking The package is effectively abandoned, with no updates since August 2018. It is highly unlikely to be compatible with modern TypeScript versions (e.g., TS 5.x, 6.x) or recent Node.js releases, leading to potential type mismatches, runtime errors, or unexpected behavior due to API changes in the TypeScript compiler itself.
  Fix: Consider using alternative, actively maintained libraries for programmatic TypeScript diagnostics, or interact directly with the `typescript` package API if a wrapper is not strictly necessary. Attempting to use this package with recent TypeScript versions will likely require significant polyfilling or workarounds.
• gotcha While the README uses an ESM `import` statement, the package's age and `engines.node` requirement (>=6) suggest it may ship as CommonJS. Consuming it in a pure ESM Node.js project without a build step or explicit module configuration might lead to `require is not defined` or `Cannot find module` errors.
  Fix: If encountering module resolution issues in an ESM project, verify the package's actual output format. You may need to adjust your `tsconfig.json`'s `module` and `moduleResolution` options, use a bundler, or resort to dynamic `import()` for CommonJS modules in an ESM context.

Install

• npm install typescript-service npm
• yarn add typescript-service yarn
• pnpm add typescript-service pnpm

Imports

• createService
  wrong:

  const { createService } = require('typescript-service');

  correct:

  import { createService } from 'typescript-service';

  The package's usage example in the README uses ES module syntax. However, given its publish date (2018) and Node.js engine requirement (>=6), it likely ships as CommonJS or expects bundling. Direct ESM consumption in modern Node.js might require specific module resolution configurations.
• ts.Program, ts.DiagnosticWithLocation
  wrong:

  const ts = require('typescript');

  correct:

  import * as ts from 'typescript';

  These types and objects are fundamental to the `typescript-service` API but are exposed directly from the `typescript` package, which is an implicit peer dependency.

Quickstart

Demonstrates initializing the TypeScript service and retrieving diagnostic messages for a specific file, also showing access to the underlying `ts.Program`.

import { createService } from 'typescript-service';
import * as path from 'path';

const projectRoot = process.cwd();
const configFile = path.join(projectRoot, 'tsconfig.json');
const exampleFile = path.join(projectRoot, 'src', 'example.ts');

// Ensure a tsconfig.json exists for demonstration
// In a real project, this file would be present.
// For quick testing, you might need to create a minimal tsconfig.json and src/example.ts
// e.g., tsconfig.json: { "compilerOptions": { "target": "es5", "module": "commonjs", "strict": true } }
// e.g., src/example.ts: export const a: string = 123; // This will produce a diagnostic

const service = createService({ configFile });
const diagnostics = service.getDiagnostics(exampleFile);

if (diagnostics.length > 0) {
  console.log(`Diagnostics for ${exampleFile}:`);
  diagnostics.forEach(diagnostic => {
    const message = typeof diagnostic.messageText === 'string'
      ? diagnostic.messageText
      : diagnostic.messageText.messageText;
    console.log(`  [TS${diagnostic.code}] ${message} (Line: ${diagnostic.start?.line + 1}, Char: ${diagnostic.start?.character + 1})`);
  });
} else {
  console.log(`No diagnostics found for ${exampleFile}.`);
}

// You can also get the underlying ts.Program instance
const program = service.getProgram();
console.log(`
TypeScript program contains ${program.getSourceFiles().length} source files.`);