Add hasSchema function

Author: jdesrosiers

README.md

@@ -201,6 +201,9 @@ Schema, such as `@hyperjump/json-schema/draft-2020-12`.
 * **unregisterSchema**: (uri: string) => void
 
     Remove a schema from the local schema registry.
+* **hasSchema**: (uri: string) => boolean
+
+    Check if a schema with the given URI is already registered.
 * _(deprecated)_ **addSchema**: (schema: object, retrievalUri?: string, defaultDialectId?: string) => void
 
     Load a schema manually rather than fetching it from the filesystem or over

lib/index.d.ts

@@ -8,6 +8,7 @@ export type SchemaObject = { // eslint-disable-line @typescript-eslint/consisten
 
 export const registerSchema: (schema: SchemaObject | boolean, retrievalUri?: string, contextDialectId?: string) => void;
 export const unregisterSchema: (retrievalUri: string) => void;
+export const hasSchema: (uri: string) => boolean;
 
 /**
  * @deprecated since 1.7.0. Use registerSchema instead.

lib/index.js

@@ -130,7 +130,7 @@ addKeyword(vocabulary);
 addKeyword(writeOnly);
 
 export { addSchema, unregisterSchema, validate, FLAG } from "./core.js";
-export { registerSchema } from "./schema.js";
+export { registerSchema, hasSchema } from "./schema.js";
 export {
   getMetaSchemaOutputFormat,
   setMetaSchemaOutputFormat,

lib/schema.js

@@ -59,6 +59,8 @@ export const unregisterSchema = (uri) => {
   delete schemaRegistry[normalizedUri];
 };
 
+export const hasSchema = (uri) => uri in schemaRegistry;
+
 export const buildSchemaDocument = (schema, id, dialectId, embedded = {}) => {
   // Dialect / JSON Schema Version
   if (typeof schema.$schema === "string") {