If using create-react-app, without a specific browserlist, the compiler tries to compile for older browser versions.

BigInts are not supported by all browser versions, but are still used in many libraries

This means that you may see the following error when trying to run your react app: Cannot convert a BigInt value to a number

Here is one example in the wild: https://github.com/0xs34n/starknet.js/issues/37#issuecomment-955797303

If you see the error, you can fix it by instructing your compiler to target only recent browser versions. You do this by adding the following to your package.json:

  “browserslist”: {
    “production”: [
    “chrome >= 67”,
    “edge >= 79",
    “firefox >= 68”,
    “opera >= 54",
    “safari >= 14”
    “development”: [
    “last 1 chrome version”,
    “last 1 firefox version”,
    “last 1 safari version”

As a precaution, better to also rm -rf node_modules/.cache before building or running your application again.