FeatureLayer.addAttachment() is returning the HTML response with a feature service hosted on an enterprise environment.

参考情報

対処法

Add the following bolded line of code to the HTML form:

<form id="importFileForm">

   Upload a file: <input type="file" name="attachment" id="fileinput">

   <input type="hidden" name="f" value="json">

 </form>

Or if using FormData class use the following code:

let form = new FormData();

form.set("attachment",file);

form.append("f","json");

再現の手順