Add an option to prefix an endpoint path with an environment variable. (

#85)

Co-authored-by: feugy <[email protected]>

packages/web/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@vercel/speed-insights",
-  "version": "1.1.0",
+  "version": "1.2.0-canary.1",
   "description": "Speed Insights is a tool for measuring web performance and providing suggestions for improvement.",
   "keywords": [
     "speed-insights",

packages/web/src/generic.ts

@@ -7,6 +7,7 @@ const SCRIPT_URL = 'https://va.vercel-scripts.com/v1/speed-insights';
 const PROD_SCRIPT_URL = `${SCRIPT_URL}/script.js`;
 const DEV_SCRIPT_URL = `${SCRIPT_URL}/script.debug.js`;
 const PROXY_SCRIPT_URL = '/_vercel/speed-insights/script.js';
+const basepathVariableName = 'NEXT_PUBLIC_SPEED_INSIGHTS_BASEPATH';
 
 /**
  * Injects the Vercel Speed Insights script into the page head and starts tracking page views. Read more in our [documentation](https://vercel.com/docs/speed-insights).
@@ -57,6 +58,8 @@ function injectSpeedInsights(
   }
   if (props.endpoint) {
     script.dataset.endpoint = props.endpoint;
+  } else if (process.env[basepathVariableName]) {
+    script.dataset.endpoint = `/${process.env[basepathVariableName]}/_vercel/speed-insights/vitals`;
   }
   if (props.dsn) {
     script.dataset.dsn = props.dsn;