KnownHelpersOnly flag limits helper usage to built‑in helpers only

KnownHelpersOnly flag limits helper usage to built‑in helpers only

In a repeatable CI/CD pipeline I precompile Handlebars templates with the --knownHelpersOnly flag to eliminate the compiler from production bundles and enable aggressive dead‑code elimination. The goal is a deterministic, minimal runtime bundle that satisfies a strict CSP (no unsafe-eval) and keeps template size under 5 KB gzipped.

Constraints:

• Only built‑in helpers (if, unless, each, with, lookup, log, blockHelperMissing, helperMissing) may be referenced in the templates.
• Partials must be inlined at compile time; runtime partial lookup is disallowed.
• Dynamic helper or partial names (e.g., {{{var}}} or {{> (lookup . "p")}}) are incompatible with --knownHelpersOnly.

Uncertainty arises when a template requires custom logic or dynamic references while still needing the minimal bundle.

Specific questions

• Does Handlebars provide a way to declare custom helpers for use with --knownHelpersOnly, and if so, how are they registered?
• When using --knownHelpersOnly, must all partials be passed explicitly to the precompiler, or can the CLI discover them automatically?
• What is the runtime behavior if a template contains a dynamic helper name or partial name while --knownHelpersOnly is enabled?