gulpfile.js

const gulp = require("gulp");
const eslint = require("gulp-eslint");
const compiler = require("webpack");
const webpack = require("webpack-stream");
const watch = require("gulp-watch");
const karma = require("karma");

const parseConfig = karma.config.parseConfig;
const KarmaServer = karma.Server;

const webpackConfig = require("./webpack.config.js");

const source = ["src/**/*.js"];

const test = source.concat(["test/**/*.spec.js"]);

gulp.task("pack", function () {
  return gulp
    .src("src/index.js")
    .pipe(
      webpack(webpackConfig, compiler, function (_err, _stats) {
        /* Use stats to do more things if needed */
      })
    )
    .pipe(gulp.dest("build/"));
});

gulp.task("lint", function () {
  return (
    gulp
      // Define the source files
      .src("src/**/*.js")
      .pipe(eslint({}))
      // Output the results in the console
      .pipe(eslint.format())
  );
});

gulp.task("karma", function (done) {
  parseConfig(
    __dirname + "/karma.conf.js",
    { files: test, singleRun: true },
    { promiseConfig: true, throwErrors: true }
  ).then(
    (karmaConfig) => {
      new KarmaServer(karmaConfig, done).start();
    },
    (_rejectReason) => {}
  );
});

gulp.task("watch-karma", function () {
  return gulp.src(test).pipe(
    karma({
      configFile: "karma.conf.js",
      action: "watch",
    })
  );
});

gulp.task("watch-build-watch", function () {
  watch(source, gulp.series("build"));
});

// Main tasks

const buildTask = gulp.series("pack");

gulp.task("default", buildTask);
gulp.task("build", buildTask);

gulp.task("test", gulp.series("build", "karma"));

gulp.task("watch-build", gulp.series("build", "watch-build-watch"));

gulp.task("watch", gulp.series("watch-build", "watch-karma"));