gistfile1.txt

import fs from "node:fs";
(function (){
    const start=process.hrtime.bigint();
    // add the absolute file path to a local copy of dats_dates.txt
    fs.readFile("file_path.txt", function(err, file){
        if (err === null) {
            const lines=file.toString("utf8").split("\n"),
                len=lines.length,
                output_raw={},
                output=[];
            let index = len,
                key="",
                keys=[];
            do {
                index = index - 1;
                key = lines[index].split("_")[0];
                if (output_raw[key] === undefined) {
                    output_raw[key] = 1;
                } else {
                    output_raw[key] = output_raw[key] + 1;
                }
            } while (index > 0);
            keys = Object.keys(output_raw);
            keys.sort(function(a,b){
                if (output_raw[a] < output_raw[b]) {
                    return - 1;
                }
                return 1;
            });
            index = keys.length;
            do {
                index = index - 1;
                output.push([keys[index], output_raw[keys[index]]]);
            } while (index > 0);
            // put absolute output file path here
            fs.writeFile("file_path.txt",JSON.stringify(output).replace(/\],/g, "],\n"),function(erw){
                if (erw === null) {
                    console.log(`Operation completed in ${Number(process.hrtime.bigint() - start) / 1e9} seconds.`);
                } else {
                    console.log(erw);
                }
            });
        } else {
            console.log(err);
        }
    });
}());