add better polyfills / auto polyfill opera + opera mini

.changeset/khaki-spoons-laugh.md

@@ -0,0 +1,5 @@
+---
+'@segment/analytics-next': patch
+---
+
+Fix 'Promise is undefined' issue with ie11 polyfill

packages/browser/src/browser/standalone.ts

@@ -75,8 +75,8 @@ if (shouldPolyfill()) {
   // load polyfills in order to get AJS to work with old browsers
   const script = document.createElement('script')
   script.setAttribute(
-    'src',
-    'https://cdnjs.cloudflare.com/ajax/libs/babel-polyfill/7.7.0/polyfill.min.js'
+    'src', // this should map to tsconfig lib. gated means "only load polyfill if feature does not exist"
+    'https://polyfill.io/v3/polyfill.min.js?features=es5,es2015,es2016,es2017,es2018,es2019,es2020&flags=gated'
   )
 
   if (document.readyState === 'loading') {

packages/browser/src/lib/browser-polyfill.ts

@@ -2,8 +2,11 @@ export function shouldPolyfill(): boolean {
   const browserVersionCompatList: { [browser: string]: number } = {
     Firefox: 46,
     Edge: 13,
+    Opera: 50,
   }
 
+  const isOperaMiniExtremeMode = (window as any).operamini // compression proxy - allows for page() calls.
+
   // Unfortunately IE doesn't follow the same pattern as other browsers, so we
   // need to check `isIE11` differently.
   // @ts-expect-error
@@ -14,10 +17,8 @@ export function shouldPolyfill(): boolean {
 
   return (
     isIE11 ||
+    isOperaMiniExtremeMode ||
     (browserVersionCompatList[browser] !== undefined &&
       browserVersionCompatList[browser] >= parseInt(version))
   )
 }
-
-// appName = Netscape IE / Edge
-// edge 13 Edge/13... same as FF