Manage different environments in a simple web project

gulpfile.js

const gulp = require('gulp');
const htmlReplace = require('gulp-html-replace')
const fs = require('fs');

const injectEnv = (env) => {
  return gulp.src('dist/index.html')
    .pipe(htmlReplace({
      'environment-vars': `<script>${fs.readFileSync(`${env}.environment.js`).toString()}</script>`
    }))
    .pipe(gulp.dest('dist'));
};

gulp.task('build:prod', () => {
  return injectEnv('prod');
});