Send File issue

For Javascript use a valid FILE object.

  interface FileMessageParams {
    new(): FileMessageParams;
    file: File;
    fileUrl: string;
    fileName: string;
    fileSize: number;
    mimeType: string;
    data: string;
    customType: string;
    thumbnailSizes: Array<ThumbnailSize>;
    mentionType: 'users' | 'channel';
    mentionedUserIds: Array<string>;
    mentionedUsers: Array<User>;
    metaArrays: Array<MessageMetaArray>;
    metaArrayKeys: Array<string>; // DEPRECATED
    pushNotificationDeliveryOption: 'default' | 'suppress';
    parentMessageId: number;
  }

Something like:

    const files = document.getElementById('attachFile').files;
    const file = files[0]; // Grab the first (this is a demo only. Need to validate not null and index)
    console.dir(file)