module.exports = {
    entry: "./src/ko-calendar.js",
    output: {
        filename: "./ko-calendar.js",
        libraryTarget: "commonjs2"
    }
}
module.exports = {
    entry: "./src/ko-calendar.js",
    output: {
        filename: "./ko-calendar.js",
        libraryTarget: "commonjs"
    }
}
Change webpack library target to commonjs