@babel/preset-typescript

This preset is recommended if you use TypeScript, a typed superset of JavaScript. It includes the following plugins:

• @babel/plugin-transform-typescript

You will need to specify --extensions ".ts" for @babel/cli & @babel/node cli’s to handle .ts files.

Example

In

const x: number = 0;

Out

const x = 0;

Installation

npm install --save-dev @babel/preset-typescript

Usage

With a configuration file (Recommended)

{
  "presets": ["@babel/preset-typescript"]
}

Via CLI

babel --presets @babel/preset-typescript script.ts

Via Node API

require("@babel/core").transformSync("code", {
  presets: ["@babel/preset-typescript"],
});

Options

isTSX

boolean, defaults to false

Forcibly enables jsx parsing. Otherwise angle brackets will be treated as typescript’s legacy type assertion var foo = <string>bar;. Also, isTSX: true requires allExtensions: true.

jsxPragma

string, defaults to React

Replace the function used when compiling JSX expressions. This is so that we know that the import is not a type import, and should not be removed.

jsxPragmaFrag

string, defaults to React.Fragment

Replace the function used when compiling JSX fragment expressions. This is so that we know that the import is not a type import, and should not be removed.

allExtensions

boolean, defaults to false

Indicates that every file should be parsed as TS, TSX, or as TS without JSX ambiguities (depending on the isTSX and disallowAmbiguousJSXLike options).

allowNamespaces

boolean, uses the default set by @babel/plugin-transform-typescript.

Added in: v7.6.0

Enables compilation of TypeScript namespaces.

allowDeclareFields

boolean, defaults to false

Added in: v7.7.0

NOTE: This will be enabled by default in Babel 8

When enabled, type-only class fields are only removed if they are prefixed with the declare modifier:

class A {
  declare foo: string; // Removed
  bar: string; // Initialized to undefined
  prop?: string; // Initialized to undefined
  prop1!: string // Initialized to undefined
}

disallowAmbiguousJSXLike

boolean, defaults to true for .mts and .cts files and to false otherwise.

Added in: v7.16.0

Even when JSX parsing is not enabled, this option disallows using syntax that would be ambiguous with JSX (<X> y type assertions and <X>() => {} type arguments). It matches the tsc behavior when parsing .mts and .mjs files.

onlyRemoveTypeImports

boolean, defaults to false

Added in: v7.9.0

When set to true, the transform will only remove type-only imports (introduced in TypeScript 3.8). This should only be used if you are using TypeScript >= 3.8.

optimizeConstEnums

boolean, defaults to false

Added in: v7.15.0

When set to true, Babel will inline enum values rather than using the usual enum output:

// Input
const enum Animals {
  Fish
}
console.log(Animals.Fish);
// Default output
var Animals;
(function (Animals) {
  Animals[Animals["Fish"] = 0] = "Fish";
})(Animals || (Animals = {}));
console.log(Animals.Fish);
// `optimizeConstEnums` output
console.log(0);

This option differs from TypeScript’s --isolatedModules behavior, which ignores the const modifier and compiles them as normal enums, and aligns Babel’s behavior with TypeScript’s default behavior.

However, when exporting a const enum Babel will compile it to a plain object literal so that it doesn’t need to rely on cross-file analysis when compiling it:

// Input
export const enum Animals {
  Fish,
}
// `optimizeConstEnums` output
export var Animals = {
  Fish: 0,
};

You can read more about configuring preset options here.