fhirpath.js

FHIRPath implementation in JavaScript.

Demo

Try it out on the demo page.

Installation:

Server-side (Node.js)

npm install –save fhirpath

const fhirpath = require('fhirpath');
// For FHIR model data (choice type support) pull in the model file:
const fhirpath_r4_model = require('fhirpath/fhir-context/r4');

Web-browser:

Download the zip file from the releases page. It contains a JavaScript file, fhirpath.min.js, which defines a global "fhirpath" variable, which you can then use as shown below. Note that this file is UTF-8 encoded, and the script needs to be loaded as such. For an example, see the browser-build/test/protractor/index.html file, which sets the page to be UTF-8.

For FHIR-specific features (e.g. handling of choice type fields), you will also want to include a second file with the desired FHIR version model data, e.g. fhirpath.r4.min.js for pulling in the R4 model. (At the moment, those files are small, but it would not be surprising if they grew as more support for FHIR type handling is added, so they are kept seperate from the main FHIRPath file.) These will define additional global variables like "fhirpath_dstu2_model", "fhirpath_stu3_model" or "fhirpath_r4_model".

Usage

// Evaluating FHIRPath
// API: evaluate(resourceObject, fhirPathExpression, environment)
// Note:  The resource will be modified by this function to add type information.
fhirpath.evaluate({"resourceType": "Patient", ...}, 'Patient.name.given');

// Environment variables can be passed in as third argument as a hash of
// name/value pairs:
fhirpath.evaluate({}, '%a - 1', {a: 5});

// To include FHIR model data (for support of choice types), pass in the model
// data object as the fourth argument:
fhirpath.evaluate({"resourceType": "Observation", "valueString": "green"},
                  'Observation.value', null, fhirpath_r4_model);

// Precompiling fhirpath - result can be reused against multiple resources
const path = fhirpath.compile('Patient.name.given');
var res2 = path({"resourceType": "Patient", ...}, {a: 5, ...});

fhirpath CLI

bin/fhirpath is a command-line tool for experimenting with FHIRPath.

curl http://www.hl7.org/fhir/patient-example-a.json  > pt.json

fhirpath --expression 'Patient.name.given' --resourceFile pt.json

> fhirpath(Patient.name.family) =>
> [
>  "Donald"
> ]

Instead of passing a filename containing the resource, the string of JSON representing the resource can be passed directly via --resourceJSON (useful if the JSON is brief).

fhirpath --expression 'a.b + 2' --resourceJSON '{"a": {"b": 1}}'

> fhirpath(a.b + 2) =>
> [
>  3
> ]

Environment variables can be passed via --variables followed by the JSON for an object with variable names as keys.

fhirpath --expression '%v + 2' --resourceJSON '{}' --variables '{"v": 5}'

> fhirpath(%v + 2) =>
> [
>  7
> ]

FHIR model data can be included via --model and the FHIR release version (in lower case, e.g., 'dstu2', 'stu3' or 'r4').

fhirpath --expression 'Observation.value' --resourceJSON '{"resourceType": "Observation", "valueString": "Green"}' --model r4

Also, you can pass in a filename or a string of JSON representing a part of the resource. In that case, you should pass in the base path from which this part of the resource was extracted.

fhirpath --basePath QuestionnaireResponse.item --expression 'answer.value' --model r4 --resourceFile questionnaire-part-example.json

> fhirpath(answer.value) =>
> [
>  "2 year"
> ]

If given just the FHIRPath expression, the utility will print the parsed tree:

fhirpath --expression 'Patient.name.given'

> ... will print fhirpath ast in yaml

Implementation Status

We are currently working on implementing version 2.0.0 of FHIRPath; some behavior may still be following the previous version, STU1.

The core parser was generated from the FHIRPath ANTLR grammar.

Completed sections:

• 3 (Path selection)
• 5.1 (Existence)
• 5.2 (Filtering and Projection) "ofType" - limited support for types (see below)
• 5.3 (Subsetting)
• 5.4 (Combining)
• 5.6 (String Manipulation)
• 5.7 (Tree Navigation)
• 5.8 (Utility Functions)
• 6.1 (Equality)
• 6.2 (Comparison)
• 6.4 (Collections)
• 6.5 (Boolean logic)
• 6.6 (Math)
• 6.8 (Operator Precedence) - handled by ANTLR parser
• 7 (Aggregates)
• 8 (Lexical Elements) - handled by ANTLR parser
• 9 (Environment Variables)

Almost completed sections:

• 5.5 (Conversion) - unimplemented methods: toDate, convertsToDate.

We are deferring handling information about FHIR resources, as much as possible, with the exception of support for choice types. This affects implementation of the following sections:

• 6.3 (Types) - "is" - limited support for types(see below), "as" is not supported yet

Also, because in JSON DateTime and Time types are represented as strings, if a string in a resource looks like a DateTime or Time (matches the regular expression defined for those types in FHIR), the string will be interpreted as a DateTime or Time.

Limited support for types:

Currently, the type of the resource property value is used to determine the type, without using the FHIR specification. This shortcut causes the following issues:

• Type hierarchy is not supported;
• FHIR.uri, FHIR.code, FHIR.oid, FHIR.id, FHIR.uuid, FHIR.sid, FHIR.markdown, FHIR.base64Binary are treated as FHIR.string;
• FHIR.unsignedInt, FHIR.positiveInt are treated as FHIR.integer;
• Also, a property could be specified as FHIR.decimal, but treated as FHIR.integer;
• For date-time related types, only FHIR.dateTime, FHIR.time, System.DateTime and System.Time are supported.

Development Notes

This section is for people doing development on this package (as opposed to using the package).

If you need to regenerate the parser from the ANTLR4 grammar (which is in parser/FHIRPath.g4), first download the ANTLR4 library from http://www.antlr.org/download/antlr-4.7.1-complete.jar into the root of the project directory, and then run "npm run generateParser".

Building the demo page

npm install && npm run build
cd demo
npm install && npm run build && npm run start

open browser on localhost:8080