You should probably never use delete. Not only it mutates objects but also have perf penalty. > If there is an interface: `interface ISomething { x?: string };

You should probably never use delete. Not only it mutates objects but also have perf penalty. > If there is an interface: `interface ISomething { x?: string };` and obj of this interface to have `obj.x = undefined` instead of `delete obj.x`. In typescript additional properties are not a problem. Since it is using structural typing. In most cases spread and restructuring are better options for merging/overwriting and deleting. It is safer and easier to reason about. > Writing methods: `function x(param0, param1?, param2?) {}` to be used as `x(1, undefined, '2');` instead of creating the func as `function x(param0, option: { param1?, param2? })` and using as `x(1, { param2: '2' })`. I am not fan of creating functions taking options objects as argument. In many cases is better to create specialized functions