async minify() {
        if (this.extension() === '.js') {
            const output = await Terser.minify(
                this.read(),
                this.mix.config.terser.terserOptions
            );

            if (output.code !== undefined) {
                this.write(output.code);
            }
        }

        if (this.extension() === '.css') {
            const output = await new UglifyCss(this.mix.config.cleanCss).minify(
                this.read()
            );

            this.write(output.styles);
        }

        return this;
    }
Minify the file, if it is CSS or JS.