Set multiple object values (`a: b: undefined`)

How about extending the pick notation?

const obj = Object.create(null)
obj.{prop1, prop2} = null
// obj.prop1 = obj.prop2 = null

// sadly the second one doesn't exactly match your interest
obj.{prop3, prop4} = getId()
// // obj.prop3 = obj.prop4 = getId()

I guess that behaviour should be implemented through loops;

for(let x of ["prop3", "prop4"])
    obj[x] = getId()