wallPhoto.js

import fetchStream from 'fetch-readablestream';

const CORS_PROXY = "https://cors-anywhere.herokuapp.com/";
const APP_ID = 9999999;

async function fetchFileStream(fileAddress, filename, imgType) {
    return fetchStream(fileAddress)
        .then(response => readAllChunks(response.body))
        .then(chunks => new File(chunks, filename, {type: imgType}));
};

const readAllChunks = (readableStream) {
    const reader = readableStream.getReader();
    const chunks = [];

    const pump = () => {
        return reader.read().then(({value, done}) => {
            if (done)
                return chunks;
            chunks.push(value);
            return pump();
        });
    }

    return pump();
}


 async function publishOnWall() {
        const authToken = await connect.send("VKWebAppGetAuthToken", {
            "app_id": APP_ID,
            "scope": "photos"
        });
        const serverToPhoto = await connect.send("VKWebAppCallAPIMethod", {
            method: "photos.getWallUploadServer",
            params: {access_token: authToken.data.access_token, v: "5.95"}
        });
        const uploadUrl = serverToPhoto.data.response.upload_url;
        const request = new FormData();
        request.append("photo", await fetchFileStream(wallPhoto, "story.png", 'image/png'));
        const {server, photo, hash} = await fetch(CORS_PROXY + uploadUrl, {
            method: "POST",
            body: request
        }).then((response) => response.json());
        const res = await connect.send("VKWebAppCallAPIMethod", {
            method: "photos.saveWallPhoto",
            params: {
                access_token: authToken.data.access_token, server, photo, hash,
                v: "5.95"
            }
        });
        const {id: photo_id, owner_id} = res.data.response[0];
        await connect.send("VKWebAppShowWallPostBox", {
            message: `Сообщение на стену с фото`,
            attachments: `photo${owner_id}_${photo_id},https://vk.com/app${APP_ID}`
        });
    }