Gulpjs has a lot of plugins that allow you to rename files. I will use gulp-rename plugin to do that.

You install the plugin as a devDependencies

npm install --save-dev gulp-rename

After installing, you import the plugin and create a task to a rename files

const { src, dest } = require("gulp");
const rename = require("gulp-rename");

const renameFile = () => {
  return src("src/js/index.js")
    .pipe(rename({ basename: "test", extname: ".min.js" }))
    .pipe(dest("src/js"));
};

exports.default = renameFile;

In my task, I rename index.js file to test.min.js file. You need to use pipe method to write your newly renamed file to the destination else it won't work

Run gulp command

gulp

After running the command, you will see test.min.js in the src/js directory. You can use gulp-rename to change dirname, add prefix or suffix to your file's name