Tygo is a tool for generating Typescript typings from Golang source files that just works.

It preserves comments, understands constants and also supports non-struct type expressions. It's perfect for generating equivalent types for a Golang REST API to be used in your front-end codebase.

🚀 Supports Golang 1.18 generic types and struct inheritance

go install github.com/gzuidhof/tygo@latest

Golang input file

// Comments are kept :)
type ComplexType map[string]map[uint16]*uint32

type UserRole = string
const (
	UserRoleDefault UserRole = "viewer"
	UserRoleEditor  UserRole = "editor" // Line comments are also kept
)

type UserEntry struct {
	// Instead of specifying `tstype` we could also declare the typing
	// for uuid.NullUUID in the config file.
	ID uuid.NullUUID `json:"id" tstype:"string | null"`

	Preferences map[string]struct {
		Foo uint32 `json:"foo"`
		// An unknown type without a `tstype` tag or mapping in the config file
		// becomes `any`
		Bar uuid.UUID `json:"bar"`
	} `json:"prefs"`

	MaybeFieldWithStar *string  `json:"address"`
	Nickname           string   `json:"nickname,omitempty"`
	Role               UserRole `json:"role"`

	Complex    ComplexType `json:"complex"`
	unexported bool        // Unexported fields are omitted
	Ignored    bool        `tstype:"-"` // Fields with - are omitted too
}

type ListUsersResponse struct {
	Users []UserEntry `json:"users"`
}

Typescript output

/**
 * Comments are kept :)
 */
export type ComplexType = {
  [key: string]: {
    [key: number /* uint16 */]: number /* uint32 */ | undefined;
  };
};
export type UserRole = string;
export const UserRoleDefault: UserRole = "viewer";
export const UserRoleEditor: UserRole = "editor"; // Line comments are also kept
export interface UserEntry {
  /**
   * Instead of specifying `tstype` we could also declare the typing
   * for uuid.NullUUID in the config file.
   */
  id: string | null;
  prefs: {
    [key: string]: {
      foo: number /* uint32 */;
      /**
       * An unknown type without a `tstype` tag or mapping in the config file
       * becomes `any`
       */
      bar: any /* uuid.UUID */;
    };
  };
  address?: string;
  nickname?: string;
  role: UserRole;
  complex: ComplexType;
}
export interface ListUsersResponse {
  users: UserEntry[];
}

For a real baptism by fire example, here is a Gist with output for the Go built-in net/http and time package.

Create a file tygo.yaml in which you specify which packages are to be converted and any special type mappings you want to add.

packages:
  - path: "github.com/gzuidhof/tygo/examples/bookstore"
    type_mappings:
      time.Time: "string /* RFC3339 */"
      null.String: "null | string"
      null.Bool: "null | boolean"
      uuid.UUID: "string /* uuid */"
      uuid.NullUUID: "null | string /* uuid */"

Then run

tygo generate

The output Typescript file will be next to the Go source files.

config := &tygo.Config{
  Packages: []*tygo.PackageConfig{
      &tygo.PackageConfig{
          Path: "github.com/gzuidhof/tygo/examples/bookstore",
      },
  },
}
gen := tygo.New(config)
err := gen.Generate()

# You can specify more than one package
packages:
  # The package path just like you would import it in Go
  - path: "github.com/my/package"

    # Where this output should be written to.
    # If you specify a folder it will be written to a file `index.ts` within that folder. By default it is written into the Golang package folder.
    output_path: "webapp/api/types.ts"

    # Customize the indentation (use \t if you want tabs)
    indent: "    "

    # Specify your own custom type translations, useful for custom types, `time.Time` and `null.String`.
    # Be default unrecognized types will be `any`.
    type_mappings:
      time.Time: "string"
      my.Type: "SomeType"

    # This content will be put at the top of the output Typescript file, useful for importing custom types.
    frontmatter: |
      "import {SomeType} from "../lib/sometype.ts"

    # Filenames of Go source files that should not be included
    # in the output.
    exclude_files:
      - "private_stuff.go"

    # Package that the generates Typescript types should extend. This is useful when
    # attaching your types to a generic ORM.
    extends: "SomeType"

See also the source file tygo/config.go.

You can tag struct fields with tstype to specify their output Typescript type.

// Golang input

type Book struct {
	Title    string    `json:"title"`
	Genre    string    `json:"genre" tstype:"'novel' | 'crime' | 'fantasy'"`
}

// Typescript output

export interface Book {
  title: string;
  genre: "novel" | "crime" | "fantasy";
}

Alternative

You could use the frontmatter field in the config to inject export type Genre = "novel" | "crime" | "fantasy" at the top of the file, and use tstype:"Genre". I personally prefer that as we may use the Genre type more than once.

tygo:emit directive

Another way to generate types that cannot be directly represented in Go is to use a //tygo:emit directive to directly emit literal TS code. The directive can be used in two ways. A tygo:emit directive on a struct will emit the remainder of the directive text before the struct.

// Golang input

//tygo:emit export type Genre = "novel" | "crime" | "fantasy"
type Book struct {
	Title    string    `json:"title"`
	Genre    string    `json:"genre" tstype:"Genre"`
}

export type Genre = "novel" | "crime" | "fantasy"

export interface Book {
  title: string;
  genre: Genre;
}

A //tygo:emit directive on a string var will emit the contents of the var, useful for multi-line content.

//tygo:emit
var _ = `export type StructAsTuple=[
  a:number, 
  b:number, 
  c:string,
]
`
type CustomMarshalled struct {
  Content []StructAsTuple `json:"content"`
}

export type StructAsTuple=[
  a:number, 
  b:number, 
  c:string,
]

export interface CustomMarshalled {
  content: StructAsTuple[];
}

Generating types this way is particularly useful for tuple types, because a comma cannot be used in the tstype tag.

Pointer type fields usually become optional in the Typescript output, but sometimes you may want to require it regardless.

You can add ,required to the tstype tag to mark a pointer type as required.

// Golang input
type Nicknames struct {
	Alice   *string `json:"alice"`
	Bob     *string `json:"bob" tstype:"BobCustomType,required"`
	Charlie *string `json:"charlie" tstype:",required"`
}

// Typescript output
export interface Nicknames {
  alice?: string;
  bob: BobCustomType;
  charlie: string;
}

Sometimes a field should be immutable, you can add ,readonly to the tstype tag to mark a field as readonly.

// Golang input
type Cat struct {
	Name    string `json:"name,readonly"`
	Owner   string `json:"owner"`
}

// Typescript output
export interface Cat {
  readonly name: string;
  owner: string;
}

Tygo supports interface inheritance. To extend an inlined struct, use the tag tstype:",extends" on struct fields you wish to extend. Only struct types can be extended.

Struct pointers are optionally extended using Partial<MyType>. To mark these structs as required, use the tag tstype:",extends,required".

Named struct fields can also be extended.

Example usage here

// Golang input
import "example.com/external"

type Base struct {
	Name string `json:"name"`
}

type Base2[T string | int] struct {
	ID T `json:"id"`
}

type OptionalPtr struct {
	Field string `json:"field"`
}

type Other[T int] struct {
	*Base                  `       tstype:",extends,required"`
	Base2[T]               `       tstype:",extends"`
	*OptionalPtr           `       tstype:",extends"`
	external.AnotherStruct `       tstype:",extends"`
	OtherValue             string `                  json:"other_value"`
}

// Typescript output
export interface Base {
  name: string;
}

export interface Base2<T extends string | number /* int */> {
  id: T;
}

export interface OptionalPtr {
  field: string;
}

export interface Other<T extends number /* int */>
  extends Base,
    Base2<T>,
    Partial<OptionalPtr>,
    external.AnotherStruct {
  other_value: string;
}

Tygo supports generic types (Go version >= 1.18) out of the box.

// Golang input
type UnionType interface {
	uint64 | string
}

type ABCD[A, B string, C UnionType, D int64 | bool] struct {
	A A `json:"a"`
	B B `json:"b"`
	C C `json:"c"`
	D D `json:"d"`
}

// Typescript output
export type UnionType = number /* uint64 */ | string;

export interface ABCD<
  A extends string,
  B extends string,
  C extends UnionType,
  D extends number /* int64 */ | boolean
> {
  a: A;
  b: B;
  c: C;
  d: D;
}

Tygo supports generating typings for YAML-serializable objects that can be understood by Go apps.

By default, Tygo will respect yaml Go struct tags, in addition to json, but it will not apply any transformations to untagged fields. However, the default behavior of the popular gopkg.in/yaml.v2 package for Go structs without tags is to downcase the struct field names. To emulate this behavior, one can use the flavor configuration option:

packages:
  - path: "github.com/my/package"
    output_path: "webapp/api/types.ts"
    flavor: "yaml"

// Golang input
type Foo struct {
	TaggedField string `yaml:"custom_field_name_in_yaml"`
    UntaggedField string
}

// Typescript output
export interface Foo {
  custom_field_name_in_yaml: string;
  untaggedfield: string;
}

• typescriptify-golang-structs: Probably the most popular choice. The downside of this package is that it relies on reflection rather than parsing, which means that certain things can't be kept such as comments without adding a bunch of tags to your structs. The CLI generates a Go file which is then executed and reflected on. The library requires you to manually specify all types that should be converted.
• go2ts: A transpiler with a web interface, this project can be seen as an evolution of this project. It's perfect for quick one-off transpilations. There is no CLI, no support for const and there are no ways to customize the output.

If tygo is useful for your project, consider leaving a star.

MIT