DFS 10.4.0 - JSS Integration - Code-First Workflow
In a code-first workflow the JSS app creates a manifest of its content data and data schema, from a set of files. This enables the JSS app to execute with local mock content, without a Sitecore instance. In this mode the JSS app is the master copy of all artifacts. The manifest gets imported into Sitecore which creates the necessary structures to support the app.
Code-first workflow makes sense to select when:
Early prototyping of a design, where a Sitecore instance may not be available to deploy to.
The primary developers on the team are JavaScript developers.
Frontend developers will not have their own Sitecore instances.
The needs of the app are relatively simple from a content perspective.
Hiring an external frontend agency to build a JSS app that will later be integrated to Sitecore.