If you want it to work in Safari or Edge (or other ES6 compliant browsers), you can use Object.assign(foo, {'a': 'b', etc.}) Instead of {...foo, 'a':

If you want it to work in Safari or Edge (or other ES6 compliant browsers), you can use Object.assign(foo, {'a': 'b', etc.}) Instead of {...foo, 'a': 'b', etc.} For example, https://beta.observablehq.com/d/64da99d0a15ecb6a https://beta.observablehq.com/d/64da99d0a15ecb6a