Bundless works differently when in development and in build, to share as much logic as possible bundless encapsulates as much logic as possible in plugins.
The bundless Plugin interface is a superset of esbuild's plugin interface, this means that the same plugins can be used both when running in development and in build phase.
Esbuild is not only used in the build phase, it is also used to traverse the module graph in the prebundle phase and to bundle dependencies.
The prebundle phase consists in
traverse the module import graph
gather all imports to files in node_modules
bundle these files in valid ES modules
store them in the web_modules directory
The prebundle phase is necessary to make commonjs code work in the browser and reduce the number of network requests to fetch modules.
In development bundless is a web server that serves your modules to the browser.
It also has does some built in transformations to your files
import paths are rewritten to path on root, import './file' becomes import '/path/to/file.js'
import paths are resolved to their path s
plugins onLoad and onTransform methods are called on the module contents
When building the entries are passed to esbuild to be bundles
Html files are converted to js files that import their scripts src urls (only those that are inside your root directory)