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    OpenAPI Typescript Codegen

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    Node.js library that generates Typescript clients based on the OpenAPI specification.


    • Frontend ❤️ OpenAPI, but we do not want to use JAVA codegen in our builds
    • Quick, lightweight, robust and framework agnostic 🚀
    • Supports generation of TypeScript clients
    • Supports generations of fetch and XHR http clients
    • Supports OpenAPI specification v2.0 and v3.0
    • Supports JSON and YAML files for input
    • Supports generation through CLI, Node.js and NPX
    • Supports tsc and @babel/plugin-transform-typescript


    npm install openapi-typescript-codegen --save-dev


    $ openapi --help
      Usage: openapi [options]
        -V, --version             output the version number
        -i, --input <value>       OpenAPI specification, can be a path, url or string content (required)
        -o, --output <value>      Output directory (required)
        -c, --client <value>      HTTP client to generate [fetch, xhr, node] (default: "fetch")
        --useOptions              Use options instead of arguments
        --useUnionTypes           Use union types instead of enums
        --exportCore <value>      Write core files to disk (default: true)
        --exportServices <value>  Write services to disk (default: true)
        --exportModels <value>    Write models to disk (default: true)
        --exportSchemas <value>   Write schemas to disk (default: false)
        $ openapi --input ./spec.json
        $ openapi --input ./spec.json --output ./dist
        $ openapi --input ./spec.json --output ./dist --client xhr



        "scripts": {
            "generate": "openapi --input ./spec.json --output ./dist"


    npx openapi-typescript-codegen --input ./spec.json --output ./dist

    Node.js API

    const OpenAPI = require('openapi-typescript-codegen');
        input: './spec.json',
        output: './dist'
    // Or by providing the content of the spec directly 🚀
        input: require('./spec.json'),
        output: './dist'


    Argument style vs. Object style --useOptions

    There's no named parameter in JavaScript or TypeScript, because of that, we offer the flag --useOptions to generate code in two different styles.


    function createUser(name: string, password: string, type?: string, address?: string) {
        // ...
    // Usage
    createUser('Jack', '123456', undefined, 'NY US');


    function createUser({ name, password, type, address }: {
        name: string,
        password: string,
        type?: string
        address?: string
    }) {
        // ...
    // Usage
        name: 'Jack',
        password: '123456',
        address: 'NY US'

    Enums vs. Union Types --useUnionTypes

    The OpenAPI spec allows you to define enums inside the data model. By default, we convert these enums definitions to TypeScript enums. However, these enums are merged inside the namespace of the model, this is unsupported by Babel, see docs. Because we also want to support projects that use Babel @babel/plugin-transform-typescript, we offer the flag --useOptions to generate union types instead of the traditional enums. The difference can be seen below:


    // Model
    export interface Order {
        id?: number;
        quantity?: number;
        status?: Order.status;
    export namespace Order {
        export enum status {
            PLACED = 'placed',
            APPROVED = 'approved',
            DELIVERED = 'delivered',
    // Usage
    const order: Order = {
        id: 1,
        quantity: 40,
        status: Order.status.PLACED

    Union Types:

    // Model
    export interface Order {
        id?: number;
        quantity?: number;
        status?: 'placed' | 'approved' | 'delivered';
    // Usage
    const order: Order = {
        id: 1,
        quantity: 40,
        status: 'placed'

    Runtime schemas --exportSchemas

    By default, the OpenAPI generator only exports interfaces for your models. These interfaces will help you during development, but will not be available in JavaScript during runtime. However, Swagger allows you to define properties that can be useful during runtime, for instance: maxLength of a string or a pattern to match, etc. Let's say we have the following model:

        "MyModel": {
            "required": [
            "type": "object",
            "properties": {
                "key": {
                    "maxLength": 64,
                    "pattern": "^[a-zA-Z0-9_]*$",
                    "type": "string"
                "name": {
                    "maxLength": 255,
                    "type": "string"
                "enabled": {
                    "type": "boolean",
                    "readOnly": true
                "modified": {
                    "type": "string",
                    "format": "date-time",
                    "readOnly": true

    This will generate the following interface:

    export interface MyModel {
        key: string;
        name: string;
        readonly enabled?: boolean;
        readonly modified?: string;

    The interface does not contain any properties like maxLength or pattern. However, they could be useful if we wanted to create some form where a user could create such a model. In that form you would iterate over the properties to render form fields based on their type and validate the input based on the maxLength or pattern property. This requires us to have this information somewhere... For this we can use the flag --exportSchemas to generate a runtime model next to the normal interface:

    export const $MyModel = {
        properties: {
            key: {
                type: 'string',
                isRequired: true,
                maxLength: 64,
                pattern: '^[a-zA-Z0-9_]*$',
            name: {
                type: 'string',
                isRequired: true,
                maxLength: 255,
            enabled: {
                type: 'boolean',
                isReadOnly: true,
            modified: {
                type: 'string',
                isReadOnly: true,
                format: 'date-time',

    These runtime object are prefixed with a $ character and expose all the interesting attributes of a model and its properties. We can now use this object to generate the form:

    import { $MyModel } from './generated';
    // Some pseudo code to iterate over the properties and return a form field
    // the form field could be some abstract component that renders the correct
    // field type and validation rules based on the given input.
    const formFields = Object.entries($[key, value]) => (
    const MyForm = () => (

    Enum with custom names and descriptions

    You can use x-enum-varnames and x-enum-descriptions in your spec to generate enum with custom names and descriptions. It's not in official spec yet. But it's a supported extension that can help developers use more meaningful enumerators.

        "EnumWithStrings": {
            "description": "This is a simple enum with strings",
            "enum": [
            "x-enum-varnames": [
            "x-enum-descriptions": [
                "Used when the status of something is successful",
                "Used when the status of something has a warning",
                "Used when the status of something has an error"

    Generated code:

    enum EnumWithStrings {
        * Used when the status of something is successful
        Success = 0,
        * Used when the status of something has a warning
        Waring = 1,
        * Used when the status of something has an error
        Error = 2,


    The OpenAPI generator supports Bearer Token authorization. In order to enable the sending of tokens in each request you can set the token using the global OpenAPI configuration:

    import { OpenAPI } from './generated';
    OpenAPI.TOKEN = 'some-bearer-token';

    Compare to other generators

    Depending on which swagger generator you use, you will see different output. For instance: Different ways of generating models, services, level of quality, HTTP client, etc. I've compiled a list with the results per area and how they compare against the openapi-typescript-codegen.

    Click here to see the comparison


    Babel support

    If you use enums inside your models / definitions then those enums are by default inside a namespace with the same name as your model. This is called declaration merging. However, the @babel/plugin-transform-typescript does not support these namespaces, so if you are using babel in your project please use the --useUnionTypes flag to generate union types instead of traditional enums. More info can be found here: Enums vs. Union Types.

    Note: If you are using Babel 7 and Typescript 3.8 (or higher) then you should enable the onlyRemoveTypeImports to ignore any 'type only' imports, see for more info

    module.exports = {
        presets: [
            ['@babel/preset-typescript', {
                onlyRemoveTypeImports: true,

    Node.js support

    By default, this library will generate a client that is compatible with the (browser based) fetch API, however this client will not work inside the Node.js environment. If you want to generate a Node.js compatible client then you can specify --client node in the openapi call:

    openapi --input ./spec.json --output ./dist --client node

    This will generate a client that uses node-fetch internally. However, in order to compile and run this client, you will need to install the node-fetch dependencies:

    npm install @types/node-fetch --save-dev
    npm install node-fetch --save-dev
    npm install form-data --save-dev


    npm i @beatgig/openapi-typescript-codegen

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