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Installing the npm module

npm install --save @sozialhelden/a11yjson


A11yJSON's reference provides a documentation of all available interfaces and has example A11yJSON objects.

For each interface X you find in the reference, the a11yjson npm module provides

  1. a TypeScript interface X (if you use TypeScript)
  2. a SimpleSchema instance named XSchema to validate and sanitize objects to be correct A11yJSON

TypeScript usage

import { PlaceInfo } from '@sozialhelden/a11yjson';

const placeInfo: PlaceInfo = {
  geometry: { type: Point, coordinates: [2.376757, 48.898991] },
  properties: {
    category: "cinema",
    name: "Ciné XY",
    accessibility: {
      accessibleWith: {
        guideDog: true,
        wheelchair: true,
      media: [
          type: 'movie',
          interactions: {
            watch: {
              perception: {
                languages: ['fr'],
                dedicatedScreenForSubtitles: true,
                subtitles: true,
                audioDescription: true,
                byod: true,
                educationLevel: 3,
                visual: true,
                realTimeCaptioning: true,
                signLanguage: true,

The TypeScript compiler will validate definitions at compile time.

Validating A11yJSON objects at runtime

The following code imports one interface schema, PlaceInfoSchema, from A11yJSON, and validates an object against it.

If the object isn't valid, you get a detailed error object as validation result.

import { getPlaceInfoSchemaDefinition } from '@sozialhelden/a11yjson';

const PlaceInfoSchema = new SimpleSchema(getPlaceInfoSchemaDefinition());

// This could be your GeoJSON feature.

const myGeoJSONFeature = {
  geometry: {  }
  properties: {  }

// See for the full documentation
// of how validation works.

const validationContext = PlaceInfoSchema.newContext();

// Sanitizes the input object.
// Converts types to match the schema where possible, and converts quantity
// strings like '12 inches' to Quantity objects like { value: 12, unit: 'inch' }.

const sanitizedGeoJSONFeature = PlaceInfoSchema.clean(myGeoJSONFeature);

// Checks if the GeoJSON is a valid A11yJSON’s `PlaceInfo`.


if (!validationContext.isValid()) {
  const errors = validationContext.validationErrors();

  // `errors` is a JSON object with detailled validation infos about each field
  // in the input object.