@babel/plugin-transform-typescript 8.x

Complete instructions

Verified against @babel/plugin-transform-typescript@8.0.1 on 2026-09-08. 4 of 4 examples executed.

@babel/plugin-transform-typescript

Scope

The resolved version is 8.0.0. The package is ESM and has one default runtime export: the Babel plugin. It has no named runtime exports. The only documented subpath is @babel/plugin-transform-typescript/package.json.

Use it with Babel 8's @babel/core; the plugin itself is not a runner. A compatible Babel core is required—do not mix Babel 7 and Babel 8 major versions. The plugin transforms TypeScript syntax but does not type-check input.

import assert from "node:assert/strict";
import { transformSync } from "@babel/core";
import transformTypeScript from "@babel/plugin-transform-typescript";

const result = transformSync("const value: number = 0;", {
  plugins: [transformTypeScript],
});

assert.ok(result?.code);
assert.match(result.code, /const value = 0/);
assert.doesNotMatch(result.code, /: number/);

Basic transformation

The plugin removes TypeScript-only annotations. It does not provide general JavaScript transpilation, module lowering, JSX transformation, or polyfills; combine it with the relevant Babel plugins or presets when those are needed.

import assert from "node:assert/strict";
import { transformSync } from "@babel/core";
import transformTypeScript from "@babel/plugin-transform-typescript";

const result = transformSync(
  `
  const count: number = 0;
  class A {
    declare foo: string;
    bar: string;
  }
  `,
  { plugins: [transformTypeScript] },
);

assert.ok(result?.code);
assert.match(result.code, /const count = 0/);
assert.match(result.code, /class A/);
assert.doesNotMatch(result.code, /declare/);
assert.doesNotMatch(result.code, /foo/);
assert.match(result.code, /bar/);

Babel 8 typed class fields

In Babel 8, an uninitialized typed class field remains a runtime field. Use declare for a type-only field that should be removed. Do not carry forward the older Babel 7 allowDeclareFields configuration; Babel 8 enables this behavior by default.

The transformed output may represent the remaining uninitialized field as a bare class field such as foo;; do not require an explicit undefined initializer.

import assert from "node:assert/strict";
import { transformSync } from "@babel/core";
import transformTypeScript from "@babel/plugin-transform-typescript";

const result = transformSync(
  `class A {
    foo: string | void;
    declare bar: number;
  }`,
  { plugins: [transformTypeScript] },
);

assert.ok(result?.code);
assert.match(result.code, /foo/);
assert.doesNotMatch(result.code, /declare/);
assert.doesNotMatch(result.code, /bar/);

const enum optimization

Set optimizeConstEnums: true to inline a const enum member use.

import assert from "node:assert/strict";
import { transformSync } from "@babel/core";
import transformTypeScript from "@babel/plugin-transform-typescript";

const result = transformSync(
  `const enum Animals { Fish }
   console.log(Animals.Fish);`,
  {
    plugins: [[transformTypeScript, { optimizeConstEnums: true }]],
  },
);

assert.ok(result?.code);
assert.match(result.code, /console\.log\(0\)/);
assert.doesNotMatch(result.code, /Animals\.Fish/);

Options and configuration mistakes

The plugin options are:

• allowNamespaces?: boolean
• jsxPragma?: string, defaulting to React.createElement
• jsxPragmaFrag?: string, defaulting to React.Fragment
• onlyRemoveTypeImports?: boolean
• optimizeConstEnums?: boolean

In Babel 8, onlyRemoveTypeImports defaults to true. If using TypeScript before 3.8, or not using verbatimModuleSyntax: true, explicitly configure onlyRemoveTypeImports: false.

Pass options as the second item in a Babel plugin tuple:

plugins: [[transformTypeScript, { onlyRemoveTypeImports: false }]]

Do not use the older preset-oriented isTSX or allExtensions configuration in Babel 8. Babel 8 uses file extensions plus JSX plugin or preset configuration. For a nonstandard extension, use ignoreExtensions: true.

The package is also included in @babel/preset-typescript, but installing or using the preset does not add type-checking.

CommonJS import = require caveat

TypeScript's import alias = require("foo") form is intended for compilation to CommonJS. Running only this plugin through transformSync does not provide that module-compilation context and can report that the form is supported only when compiling modules to CommonJS. Configure the appropriate Babel module transformation as part of the toolchain; the TypeScript plugin alone is not a complete module compiler.

This part is therefore not demonstrated by a standalone example here: the required CommonJS module-compilation setup is outside the package's standalone transform-only behavior covered by this skill.

Does not cover

This skill does not cover TypeScript type-checking, JSX transformation details, module lowering or complete CommonJS module compilation, polyfills, general ES-feature transpilation, Babel CLI invocation, preset configuration beyond the migration points above, or the complete behavior of every plugin option. Those require the relevant TypeScript or Babel tools and configuration.