index.js

const { Index } = require("flexsearch");

(async function(){

    // you will need to keep the index configuration
    // they will not export, also every change to the
    // configuration requires a full re-index
    const config = {
        tokenize: "forward"
    };

    // create a simple index which can store id-content-pairs
    let index = new Index(config);

    // some test data
    const data = [
        'cats abcd efgh ijkl mnop qrst uvwx cute',
        'cats abcd efgh ijkl mnop qrst cute',
        'cats abcd efgh ijkl mnop cute',
        'cats abcd efgh ijkl cute',
        'cats abcd efgh cute',
        'cats abcd cute',
        'cats cute'
    ];

    // add data to the index
    data.forEach((item, id) => {
        index.add(id, item);
    });

    // perform query
    let result = index.search("cute cat");

    // display results
    result.forEach(i => {
        console.log(data[i]);
    });

    // -----------------------
    // EXPORT
    // -----------------------

    const fs = require("fs").promises;

    await fs.mkdir("./export/").catch(e => {});
    await index.export(async function(key, data){
        await fs.writeFile("./export/" + key, data, "utf8");
    });

    // -----------------------
    // IMPORT
    // -----------------------

    // create the same type of index you have used by .export()
    // along with the same configuration
    index = new Index(config);

    // load them in parallel
    const files = await fs.readdir("./export/");
    await Promise.all(files.map(async file => {
        const data = await fs.readFile("./export/" + file, "utf8");
        index.import(file, data);
    }));

    // perform query
    result = index.search("cute cat");

    // display results
    console.log("-------------------------------------");
    result.forEach(i => {
        console.log(data[i]);
    });
}());