Fn to put deep __typename based on keys for apollo gql (apollo link rest is too verbose)

deep-typename-apollo.ts

/*
 * This is micro optimized, you could
 * do it without mutability, but I think
 * that this is to solve a very specific case (apollo
 * requires __typename to be injected)
 */
function addTypeNames(
  item: object,
  typeNames: object
) {
  const keys = Object.keys(item)

  for(const key of keys) {
    const typeName = typeNames[key]
    const entry = item[key]

    if(entry instanceof Array) {
      entry.forEach(listEntry => addTypeNames({ [key]: listEntry }, typeNames))

      continue
    }

    if(entry instanceof Object) {
      if(typeName) {
        entry.__typename = typeName
      } else if(__DEV__) {
        throw `'${key}' doesn't contain a key definition!`
      } else {
        // eslint-disable-next-line no-console
        console.warn(`'${key}' doesn't contain a key definition!`)
      }

      addTypeNames(entry, typeNames)
    }
  }
}


const myReturn = {
    entry: {
      deepProp:{
        foo: 2
      }
    }
}

addTypeNames({ root: myReturn }, {
  root: 'RootType'
  entry: 'EntryType'
  deepProp: 'DeepProp'
})

console.log(myReturn) 
/* ->
{
  __typename: 'RootType'
  entry: {
    __typename: 'EntryType'
    deepProp:{
      __typename: 'DeepProp'
      foo: 2
    }
  }
}
*/