Crash report: `ReferenceError: Can't find variable: ResizeObserver`

URL

https://app.uniswap.org/#/swap?origin=%2Fmigrate%2Fv2&chain=mainnet

swap state

{
  "INPUT": {
    "currencyId": "ETH"
  },
  "recipient": null,
  "OUTPUT": {
    "currencyId": "0x55296f69f40Ea6d20E478533C15A6B08B654E758"
  },
  "independentField": "OUTPUT",
  "typedValue": "5"
}

Error

ReferenceError: Can't find variable: ResizeObserver

Stacktrace

https://app.uniswap.org/static/js/3.41edfc8a.chunk.js:2:1792414
https://app.uniswap.org/static/js/3.41edfc8a.chunk.js:2:1792136
https://app.uniswap.org/static/js/3.41edfc8a.chunk.js:2:1792249
Cu@https://app.uniswap.org/static/js/3.41edfc8a.chunk.js:2:1982342
Cu@[native code]
https://app.uniswap.org/static/js/3.41edfc8a.chunk.js:2:2001553
Iu@https://app.uniswap.org/static/js/3.41edfc8a.chunk.js:2:1978962
wu@https://app.uniswap.org/static/js/3.41edfc8a.chunk.js:2:1975048
wu@[native code]
https://app.uniswap.org/static/js/3.41edfc8a.chunk.js:2:1924316
https://app.uniswap.org/static/js/3.41edfc8a.chunk.js:2:2001553
Xf@https://app.uniswap.org/static/js/3.41edfc8a.chunk.js:2:1924262
Yf@https://app.uniswap.org/static/js/3.41edfc8a.chunk.js:2:1924197
bu@https://app.uniswap.org/static/js/3.41edfc8a.chunk.js:2:1972200
Ua@https://app.uniswap.org/static/js/3.41edfc8a.chunk.js:2:1943850
Ua@[native code]
https://app.uniswap.org/static/js/main.19d4c78b.chunk.js:1:33940

Device data

{
  "ua": "Mozilla/5.0 (iPhone; CPU iPhone OS 13_3 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/13.3 Mobile/15E148 Safari/605.1",
  "browser": {
    "name": "Mobile Safari",
    "version": "13.3",
    "major": "13"
  },
  "engine": {
    "name": "WebKit",
    "version": "605.1.15"
  },
  "os": {
    "name": "iOS",
    "version": "13.3"
  },
  "device": {
    "vendor": "Apple",
    "model": "iPhone",
    "type": "mobile"
  },
  "cpu": {}
}

Start by reproducing the swap URL on Mobile Safari 13.3 on iOS 13.3 and confirm the ResizeObserver ReferenceError. Then trace the reported locations in static/js/3.41edfc8a.chunk.js and static/js/main.19d4c78b.chunk.js back to the TypeScript source. Done means the swap page no longer crashes in the reported environment.