A colleague asked me for help when he got into trouble with his TypeScript code. Here is a simplified version:
Although this looks like valid code, the TypeScript compiler complained:
After some headscratching, we discovered that there was a “rogue” tsconfig.json at a higher level that set “ES5” as the target. Object.Assign was added as part of “ES6” explaining why TypeScript complained.
After changing the target to “es6”, the error disappeared.