Unsafe argument of type `any` on presigned post fields

[reefdog]

When using the PresignedPostRequestPresignedPost type, accessing the values from a presigned post fields object triggers the ol' unsafe any type complaint:

Unsafe argument of type `any` assigned to a parameter of type `string | Blob`.

E.g.:

const uploadUsingPresignedPost = async (
    file: File,
    presignedPost: PresignedPostRequestPresignedPost,
) => {
    const formData = new FormData();
    Object.entries(presignedPost.fields).forEach(([key, value]) =>
        // ❌ This is where things break:
        formData.append(key, value),
    );
    // Rest of function omitted
}

Unsure if this should be part of https://github.com/PhilanthropyDataCommons/service/issues/1004 or is separate.

[slifty]

Now that I'm actually digging into this, this is due to the signature of Object.entries, not due to our type definition.

Object.entries cannot safely guarantee that values are always of a given type -- even if the "Type" of a given variable has only string entities documented, TypeScript is not saying there aren't more than those entities on the object (nor does it indicate what those entities will be).

So I think what we'll need to do is add a type guard e.g.:

    const isStringOrBlob(value: unknown) value is string | Blob  => typeof value  === 'string' || value instanceof Blob

    Object.entries(presignedPost.fields).forEach(([key, value]) =>
        if (isValidFormDataValue(value) {
            formData.append(key, value),
        }
    );

Here's the definition of ObjectConstructor.entries in es2017:

    /**
     * Returns an array of key/values of the enumerable properties of an object
     * @param o Object that contains the properties and methods. This can be an object that you created or an existing Document Object Model (DOM) object.
     */
    entries(o: {}): [string, any][];

^ note the any there

[slifty]

For now I'm marking this as closed as not planned based on the above analysis, that said we can absolutely re-open if that is wrong.

[reefdog]

This makes sense! Thanks for the thorough explanation and even tackling the front-end issue that this is linked to! 🙏