Why I open source my website ?
Because I can't hide source code from you.
Why I can't hide source code?
Because of the nature of internet. The nature of internet is free, the browser design inherit the nature of free internet.
The fundermental internet programming language HTML and javascript design inherit the nature of free internet.
How to get source code ?
From browser console
For example let's get source code of this model 6391.
https://transparentgov.net/json2tree/datahub.io/embed/google_streetview.html?layer_id=2&layer=Parcels¢er_lat=34.04761350116964¢er_long=-118.27351572662262¢er_zoom=19&url=https%3A%2F%2Fmaps.lacity.org%2Farcgis%2Frest%2Fservices%2FCore%2FMaster_landbase%2FMapServer&panto=0
Any webpage's source code has 3 parts.
HTML file, javascript file, and CSS file.
You only need these 3 files ( javascript and css could have multiple files)
Open browser console, click source tab, looking for these 3 parts.
Part 1. HTML is right here.
Part 2. multiple javascript file( xxxx.js) is right here
Part 3. multiple CSS file( xxxx.css) is right here
If you can get source code of my webiste, can you also use the same way to get soruce code of ESRI's COTS commercial off the shelf product's source code ?
Sure, of couse you can ! Remember internet's nature is free.
ESRI web appbuilder source code is right under your mouse click
Let's try one, looking for 3 parts html, javascript, css.
web appbuilder V3.42 was created 2019
https://gis.azdhs.gov/ephtexplorer/
Web appbuilder app, use arcgis js api V3.46
https://adhsgis.maps.arcgis.com/apps/webappviewer/index.html?id=f380818ca39d4ff98f028988366b6b0c
Experience builder's source code is compiled, not human readable, is only machine readable. This is because of experience builder is build on top of Meta's Facebook's frame work called React.js
https://experience.arcgis.com/experience/41b3ba9705084d9eb45ff583747e8845/
You can reverse engineering to convert machine readable code to human readable source code by google search multiple method, I am not going to show you how, there are many of them out there.