[BUG][Javascript] paramToString does not handle non-primitives

[tray2100]

Description

It looks like the when an API call is being constructed, the params are passed through a generic paramToString function defined here that looks like this:

exports.prototype.paramToString = function (param) {
    if (param == undefined || param == null) {
      return '';
    }
    if (param instanceof Date) {
      return param.toJSON();
    }
    return param.toString();
  };

This breaks if any of your parameters are not primitives because param.toString() will transform it into [object Object].

openapi-generator version

4.3.1 ... doesn't look to be a regression. Just missing handling

OpenAPI declaration file content or url

  /someOperation:
    post:
      requestBody:
        description: "POST request that uploads a file and takes in a metadata object"
        content:
          multipart/form-data:
            schema:
              type: "object"
              properties:
                metadata:
                  $ref: "#/components/schemas/SomeType"
                file:
                  format: "binary"
                  type: "string"
            encoding:
              metadata:
                contentType: "application/json"

Steps to reproduce

Invoke any POST operation where one parameter is a complex type (Object) using this client and the service will receive [object Object] as a value for the parameter.

Related issues/PRs

Similar issues:

• Update paramToString in Elm generator to handle other types #1079

Suggest a fix

I believe the fix should be to, as a last step, see if the parameter can be JSON-ified. If it can be, we should run JSON.stringify() on it and use that result instead of the output of param.toString(). I think a simple method like this would suffice:

exports.prototype.canBeJsonified = function(str) {
    if (typeof str !== 'string' && typeof str !== 'object') return false;
    try {
      const type = str.toString();
      return type === '[object Object]'
          || type === '[object Array]';
    } catch (err) {
      return false;
    }
  };

and we update the paramToString method to be

exports.prototype.paramToString = function(param) {
    if (param == undefined || param == null) {
      return '';
    }
    if (param instanceof Date) {
      return param.toJSON();
    }
    if (this.canBeJsonified(param)) {
      return JSON.stringify(param);
    }
    return param.toString();
  };

cc @CodeNinjai @frol @cliffano @wing328