index.js

const { Document, Charset } = require("flexsearch");
const fs = require("fs").promises;

(async function(){

    // loading test data
    const data = JSON.parse(await fs.readFile(__dirname + "/data.json", "utf8"));

    // 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 = {
        document: {
            id: "tconst",
            store: true,
            index: [{
                field: "primaryTitle",
                tokenize: "forward",
                encoder: Charset.LatinBalance
            },{
                field: "originalTitle",
                tokenize: "forward",
                encoder: Charset.LatinBalance
            }],
            tag: [{
                field: "startYear"
            },{
                field: "genres"
            }]
        }
    };

    // create the document index
    let document = new Document(config);

    // add test data
    for(let i = 0; i < data.length; i++){
        document.add(data[i]);
    }

    // perform a query
    let result = document.search({
        query: "karmen",
        tag: {
            "startYear": "1894",
            "genres": [
                "Documentary",
                "Short"
            ]
        },
        suggest: true,
        enrich: true,
        merge: true
    });

    // output results
    console.log(result);

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

    await fs.mkdir("./export/").catch(e => {});
    // call export
    await document.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
    document = new Document(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");
        // call import
        document.import(file, data);
    }))

    // perform query
    result = document.search({
        query: "karmen",
        tag: {
            "startYear": "1894",
            "genres": [
                "Documentary",
                "Short"
            ]
        },
        suggest: true,
        enrich: true,
        merge: true
    });

    // output results
    console.log("-------------------------------------");
    console.log(result);
}());