Optional Blocks

Toggle sections at runtime.

The `.optional()` Method

Define sections that can be enabled/disabled at runtime:

const summarizer = prompt("summarizer", (p) =>
  p
    .persona("expert summarizer")
    .output("concise summary")
    .optional("json", (p) =>
      p.output("valid JSON").constraint("must be parseable")
    )
);

// Use without option
summarizer.toString();

// Use with option
summarizer.toString({ json: true });

Type Safety

TypeScript knows your options:

summarizer.toString({ json: true });  // ✅
summarizer.toString({ xml: true });   // ❌ TypeScript error

Nested Optionals

const writer = prompt("writer", (p) =>
  p
    .output("content")
    .optional("format", (p) =>
      p
        .output("structured output")
        .optional("json", (p) => p.constraint("use JSON"))
        .optional("xml", (p) => p.constraint("use XML"))
    )
);

writer.toString({ format: true, json: true });

Example: Verbose Mode

const analyzer = prompt("analyzer", (p) =>
  p
    .persona("data analyst")
    .output("analysis")
    .optional("verbose", (p) =>
      p.do("include methodology").do("show confidence intervals")
    )
);

analyzer.toString();                  // quick analysis
analyzer.toString({ verbose: true }); // detailed analysis

Reusing Prompts

Share common rules across prompts.

Variables

Dynamic prompts with placeholders.

On this page

The .optional() Method Type Safety Nested Optionals Example: Verbose Mode