[typescript-fetch] (4.0.X) Model parameter uses string type when format: date

[someone1]

Description

The typescript-fetch generator defines models with type: string/format: date as type string, but serializes/deserializes the value as a Date

openapi-generator version

openapi-generator-cli-4.0.0-20181126.024631-44

OpenAPI declaration file content or url

swagger: "2.0"

paths:
  "/config":
    get:
      operationId: "config.get"
      responses:
        200:
          description: Success
          schema:
            $ref: "#/definitions/SiteConfiguration"

definitions:
  SiteConfiguration:
    description: "Site configuration"
    type: object
    properties:
      maxReportingDate:
        type: string
        format: date
      minReportingDate:
        type: string
        format: date

Generated Code (excerpt):

export interface SiteConfiguration {
    /**
     * 
     * @type {string}
     * @memberof SiteConfiguration
     */
    maxReportingDate?: string;
    /**
     * 
     * @type {string}
     * @memberof SiteConfiguration
     */
    minReportingDate?: string;
}

export function SiteConfigurationFromJSON(json: any): SiteConfiguration {
    return {
        'maxReportingDate': !exists(json, 'maxReportingDate') ? undefined : new Date(json['maxReportingDate']),
        'minReportingDate': !exists(json, 'minReportingDate') ? undefined : new Date(json['minReportingDate']),
    };
}

Command line used for generation

openapi-generator generate -i openapi.yaml -l typescript-fetch -c es6.json -o ./typescript-api/

Steps to reproduce

1. Use the provided yaml excerpt above to generate a client with the provided command line
2. Buggy code generated

Related issues/PRs

PR #569

Suggest a fix/enhancement

Add additional resolution for Date or DateTime formatted strings in getTypeDeclaration here

[macjohnny]

cc @Place1