fix: add missing Registry types (#626)

CHANGELOG.md

@@ -11,10 +11,12 @@ project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Changed
 
-- Enable `bun.js` by catching `NotImplemented` error (Fixes [#570](https://github.com/siimon/prom-client/issues/570))
+- Add `Registry.PROMETHEUS_CONTENT_TYPE` and `Registry.OPENMETRICS_CONTENT_TYPE` constants to the TypeScript types
 
 ### Added
 
+- Enable `bun.js` by catching `NotImplemented` error (Fixes [#570](https://github.com/siimon/prom-client/issues/570))
+
 [unreleased]: https://github.com/siimon/prom-client/compare/v15.1.0...HEAD
 
 ## [15.1.1] - 2024-03-26

index.d.ts

@@ -95,6 +95,16 @@ export class Registry<RegistryContentType = PrometheusContentType> {
 	 * @param registers The registers you want to merge together
 	 */
 	static merge(registers: Registry[]): Registry;
+
+	/**
+	 * HTTP Prometheus Content-Type for metrics response headers.
+	 */
+	static PROMETHEUS_CONTENT_TYPE: PrometheusContentType;
+
+	/**
+	 * HTTP OpenMetrics Content-Type for metrics response headers.
+	 */
+	static OPENMETRICS_CONTENT_TYPE: OpenMetricsContentType;
 }
 export type Collector = () => void;