Grokking Node.js Design Patterns for Interviews/

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Solution: Construct a Form Schema Builder with Validation Rules

Solution: Construct a Form Schema Builder with Validation Rules

Build a fluent, nested builder that assembles typed form fields with optional validation constraints and enforces a clean construction flow.

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Solution explanation

  • Lines 2–6: We initialize FormSchemaBuilder with an empty fields object and state flags to track defined fields, the field currently being built, and whether a field is currently being constructed.

  • Lines 8–18: .addField() enforces that no duplicate fields are added and that only one field is being built at a time. It creates a new FieldBuilder and passes in the field context.

  • Lines 20–24: _finalizeField() is called by FieldBuilder.done() to register a field definition and reset the state.

  • Lines 26–31: .build() throws if ...