serialization.ts

interface Serialized {
  a: string,
  b: string,
  c: string | string[],
 }
 
interface Deserialized {
  field: number, //parsed from a
  otherField: string, // parsed from b
  yetAnotherField: string[] // parsed from c
}

interface Field<K extends keyof Deserialized, V = K[V]> {
  parse: (serialized: Serialized) => V,
  render: (value: V) => Partial<Serialized>,
}

const fields = {
  field: {
    parse: (serialized) => Number.parseFloat(serialized.a),
    render: (value) => ({ a: value.toString() }),
  },
  // ... etc for otherField and yetAnotherField
}