MediaWiki - list all pages + properties in all namespaces.

const results = {
    pages: []
};

const promises = [];

const defaultParams = {
    action: "query",
    format: "json",
};

// Object.keys(mw.config.values.wgFormattedNamespaces).forEach((key) => {

const namespaces = [0,1,2,3,4,5,6,7,8,9];

namespaces.forEach((key) => {
    const queryParams = {
        generator: "allpages",
        gaplimit: 5000,
        gapfilterredir: "nonredirects",
        prop: "info|pageprops",
        gapnamespace: key,
        ...defaultParams,
    };
    promises.push(getInfo('pages', queryParams));
});


Promise.all(promises).then((values) => {
    console.log("Done, the file will be downloaded");

    download("results.txt", JSON.stringify(results, null, 2));
});

function getInfo(key, queryParams) {
    return new Promise((resolve) => {
        const api = new mw.Api();

        api.post(queryParams).done((data) => {
            if (data.continue) {
                const [next] = Object.entries(data.continue);
                const [continueKey, continueValue] = next;
                queryParams[continueKey] = continueValue;

                resolve(getInfo(key, queryParams));
            } else {
                resolve();
            }
            console.log("fetching data ...");
            results[key].push(data.query);
        });
    });
}

function download(filename, text) {
    var element = document.createElement("a");
    element.setAttribute(
        "href",
        "data:text/plain;charset=utf-8," + encodeURIComponent(text)
    );
    element.setAttribute("download", filename);

    element.style.display = "none";
    document.body.appendChild(element);

    element.click();

    document.body.removeChild(element);
}