My First Svelte Application: Base64 Encoder/Decoder

My First Svelte Application: Base64 Encoder/Decoder

Photo by Joshua Sortino on Unsplash

I am currently teaching myself svelte and I have enjoyed pretty much everything about it. I decided to create a simple application that encodes ASCII text or hex strings to base64, and vice-versa. In order to take advantage of svelte’s strengths, the application contains reactive UI components to help illustrate the encoding process.

I deployed this project to Netlify (click the Launch App button above to open the application in a new tab/window). I also included a button to view/fork the project with codesandbox (below), please feel free to log a github issue if you find any bugs. Thank you!

Edit svelte-base64

Base64 Encoder/Decoder

  • Input/output strings displayed in hex, decimal, binary, and base64 to demonstrate how input bytes are encoded to base64.
  • Mouseover/touch any part of the Hex/Base64 output to highlight all related bit groups and the matching base64/ASCII characters in the Lookup Tables.
  • Hex strings must contain only numbers and/or upper and lowercase hex digits (a-f, A-F, 0-9).
  • Hex strings can be prefixed by “0x”, but this is not required.
    • e.g., 0xFE and FE both represent the value 254 and both will produce the same output when encoded to base64
  • Encoded strings must be valid base64 (standard) or base64url (url/filename safe) values
  • If a decoded string is composed entirely of ASCII-printable characters, it will be rendered as text.
  • If a decoded string contains a single byte that is outside of the range of ASCII-printable characters (0x20 - 0x7E), the entire string will be rendered as hex digits.

CSS Preprocessing & Rollup Config

  • Svelte 3 + Svelma integrated via svelte-preprocess.
    • Svelma is a set of UI components for Svelte based on the Bulma CSS framework.
  • Bulma/FontAwesome 5 integrated via node-sass
  • SASS/SCSS files are bundled and copied to public/build folder (node-sass, postcss/cssnano).
  • FontAwesome font files are copied from from node_modules folder to public/webfonts folder.
  • When building for production, bundled CSS and JS files are minified.
  • resolve, commonjs, and terser rollup plugins configured.


  • Cypress E2E tests created for basic encode/decode scenarios.
  • 5 test cases are each executed with 4 different screen types/orientations.
  • Input and expected output for both ASCII and Hex strings taken directly from the Examples and Illustrations and Test Vectors sections of RFC4648 which is the original specification for Base64 and other print-safe binary encodings.
  • Github action configured to run all Cypress tests on each push to master branch, build is deployed only if all tests pass.

Automated Cypress Tests (4 Tests on 2 Screen Sizes Shown)