tsconfig.json

{
  // Although rollup-plugin-ts overrides this property when building the library,
  // it is still needed for editor plugins
  "files": ["src/index.ts"],
  "compilerOptions": {
    "target": "ES5",
    "module": "ESNext",
    "moduleResolution": "node",
    "declaration": true,
    "strict": true,

    // Without this option TS includes all the types from node_modules/@types, which
    // include ES6 types, which we don't want
    "types": [],

    // We use a subset of ES6 syntax that can be transpiled to ES5 without the need
    // for polyfills: arrow functions, template literals and destructuring. TypeScript
    // requires tslib to be imported for this even if it doesn't emit any helpers.
    // This opens up a possibility for accidentally using a feature that does emit
    // a helper without noticing it. This option could prevent this, but rollup-plugin-ts
    // overrides it, so for now we have to manually check that the output files don't
    // include any functions starting with __.
    // "noEmitHelpers": true,

    // The below properties are needed to run the tests
    "allowJs": true,
    "allowSyntheticDefaultImports": true,
    "downlevelIteration": true
  }
}