Typescript: Spread types may only be created from object types

Question

function foo<T extends object>(t: T): T {    return {     ...t // Error: [ts] Spread types may only be created from object types.   } } 

I am aware that there are issues on github, but I can't figure out what is fixed and what is not and they have 2695 open issues. So I am posting here. I am using latest Typescript 2.9.2.

Should the above code not work? And how can I fix it if possible?

Answer 1

This is fixed in TypeScript Version 3.2. See Release Notes.

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Looks like spread with a generic type isn't supported yet, but there is a GitHub issue about it: Microsoft/TypeScript#10727.

For now you can either use type assertion like @Jevgeni commented:

function foo<T extends object>(t: T): T {   return { ...(t as object) } as T; } 

or you can use Object.assign which has proper type definitions.

function foo<T extends object>(t: T): T {   return Object.assign({}, t); } 

Answer 2

You can use Record<string, unknown> or an interface like the below examples:

goodsArray.map(good => {   return {     id: good.payload.doc.id,     ...(good.payload.doc.data() as Record<string, unknown>)   }; }); 

or

goodsArray.map(good => {   return {     id: good.payload.doc.id,     ...good.payload.doc.data() as Goods // 'Goods' is my interface name   }; });