OpenAPI Typescript Codegen

NodeJS library that generates Typescript clients based on the OpenAPI specification.

Why?

• 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.

Known issues:

• If you use enums inside your models / definitions then those enums are now inside a namespace with the same name as your model. This is called declaration merging. However, Babel 7 now support compiling of Typescript and right now they do not support namespaces.

Installation

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

Example

package.json

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

Command line

npm install openapi-typescript-codegen -g

openapi --input ./api/openapi.json --output ./dist

NodeJS API

const OpenAPI = require('openapi-typescript-codegen');

OpenAPI.generate({
    input: './api/openapi.json',
    output: './generated'
});

Or by providing the JSON directly:

const OpenAPI = require('openapi-typescript-codegen');

const spec = require('./api/openapi.json');

OpenAPI.generate({
    input: spec,
    output: './generated'
});

Features

Argument-style vs. Object-style

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

Argument-style:

function createUser(name: string, password: string, type?: string, address?: string) {
    // ...
}

// Usage
createUser('Jack', '123456', undefined, 'NY US');

Object-style:

function createUser({ name, password, type, address }: {
    name: string,
    password: string,
    type?: string
    address?: string
}) {
    // ...
}

// Usage
createUser({
    name: 'Jack',
    password: '123456',
    address: 'NY US'
});

Runtime schemas

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": [
            "key",
            "name"
        ],
        "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 it's 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($MyModel.properties).map(([key, value]) => (
    <FormField
        name={key}
        type={value.type}
        format={value.format}
        maxLength={value.maxLength}
        pattern={value.pattern}
        isReadOnly={value.isReadOnly}
    />
));

const MyForm = () => (
    <form>
        {formFields}
    </form>
);

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": [
            0,
            1,
            2
        ],
        "x-enum-varnames": [
            "Success",
            "Warning"
            "Error"
        ],
        "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,
}

Authorization

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