Updated Answer:
If you are using Babel 7.4.0 or newer, then @babel/polyfill has been deprecated. Instead, you will want to use the following at the top of your main js file (likely index.js or similar):
import "core-js/stable";
import "regenerator-runtime/runtime";
Install these packages either with npm:
npm install --save core-js
npm install --save regenerator-runtime
or with yarn:
yarn add core-js
yarn add regenerator-runtime
Original Answer:
I just encountered this problem and came across the following solution:
In package.json I had @babel/polyfill as a dependency. However, in my index.js (My main js file) I had neglected to place the following line at the the top:
import '@babel/polyfill'
Once I imported it, everything worked fine.
I did not need to install babel-runtime as other answers are suggesting.