@fhir-dsl/fhirpath

Type-safe FHIRPath expression builder for TypeScript with IDE autocomplete, compilation to FHIRPath strings, and runtime evaluation.

Covers ~85% of the official FHIRPath spec including 60+ functions, expression predicates, and operators.

Install

npm install @fhir-dsl/fhirpath @fhir-dsl/types

Usage

Build expressions with autocomplete

import { fhirpath } from "@fhir-dsl/fhirpath";
import type { Patient } from "./fhir/r4"; // generated types

const expr = fhirpath<Patient>("Patient").name.family;
expr.compile();  // "Patient.name.family"

Every step in the chain is type-checked — you get autocomplete for valid property names and can't navigate to fields that don't exist.

Evaluate against resources

const families = fhirpath<Patient>("Patient").name.family.evaluate(patient);
// ["Smith", "Doe"]

Expression predicates

Use $this for filtering with where(), exists(), all(), and more:

fhirpath<Patient>("Patient")
  .name.where($this => $this.use.eq("official")).given
  .compile();
// "Patient.name.where($this.use = 'official').given"

Collection operations

fhirpath<Patient>("Patient").name.first().family.compile();
fhirpath<Patient>("Patient").name.count().compile();
fhirpath<Patient>("Patient").name.exists().compile();
fhirpath<Patient>("Patient").identifier.distinct().compile();

String, math, and conversion functions

fhirpath<Patient>("Patient").name.family.upper().compile();
fhirpath<Patient>("Patient").name.family.startsWith("Sm").compile();

`ofType()` for polymorphic fields

fhirpath<Observation>("Observation")
  .value.ofType("Quantity").value
  .compile();
// "Observation.value.ofType(Quantity).value"

Supported Functions

Navigation, filtering, subsetting, string manipulation, math, type conversion, utility, and boolean operators — 60+ FHIRPath functions are supported. See the FHIRPath docs for the full list.

License

MIT