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

$ openapi --help

  Usage: openapi [options]

  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, axios, angular] (default: "fetch")
    --name <value>            Custom client class name
    --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)
    --indent <value>          Indentation options [4, 2, tab] (default: "4")
    --postfixServices         Service name postfix (default: "Service")
    --postfixModels           Model name postfix
    --request <value>         Path to custom request file
    -h, --help                display help for command

  Examples
    $ openapi --input ./spec.json --output ./generated
    $ openapi --input ./spec.json --output ./generated --client xhr