Upload Widget - Can't add context/metadata with prepareUploadParams()

I'm trying to get the following snippet to dynamically add context/metadata to an upload through the upload widget. It needs to be dynamic because it will be pulling data from fields filled out by the user for each upload. But none of this context/metadata from this test code seems to actually get uploaded with the image, what am I doing wrong with this code? 

    prepareUploadParams: (cb, params) => {
        params["context"] = {
            "alt": "@tester, https://example.com/",
            "instagram": "@example",
            "website": "https://example.com/",
            "email": "a@example.com"
        };
        cb(params);
  }

And here is the full function that snippet is from


const myWidget = cloudinary.createUploadWidget(
  {
    cloudName: "<redacted>",
    uploadPreset: "<redacted>",
    folder: "public-upload-tester",
    cropping: true,
    sources: [
        "local",
        "url",
        "camera",
        "facebook",
        "instagram",
        "google_drive",
        "dropbox"
    ],
    tags: ["user-uploads", "public-upload-tester-content"],
    prepareUploadParams: (cb, params) => {
        params["context"] = {
            "alt": "@tester, https://example.com/",
            "instagram": "@example",
            "website": "https://example.com/",
            "email": "a@example.com"
        };
        cb(params);
    }
  },
  (error, result) => {
    if (!error && result && result.event === "success") {
      console.log("Done! Here is the image info: ", result.info);
    }
  }
);

jQuery("#upload_widget").click(function(){
    myWidget.open();
});