pb_msg_setter.ts

export function fromObject<T extends jspb.Message, U>(c: new () => T, obj: U): T {
  const instance = new c();
  Object.keys(obj)
      .forEach(key => {
        const setterName = makeSetterFuncName(key);
        (instance as any)[setterName] = (obj as any)[key];
      });
  return instance;
}

function makeSetterFuncName(key: string): string {
  switch (key) {
    case "pb_abstract":
    case "pb_boolean":
    case "pb_break":
    case "pb_byte":
    case "pb_case":
    case "pb_catch":
    case "pb_char":
    case "pb_class":
    case "pb_const":
    case "pb_continue":
    case "pb_debugger":
    case "pb_default":
    case "pb_delete":
    case "pb_do":
    case "pb_double":
    case "pb_else":
    case "pb_enum":
    case "pb_export":
    case "pb_extends":
    case "pb_false":
    case "pb_final":
    case "pb_finally":
    case "pb_float":
    case "pb_for":
    case "pb_function":
    case "pb_goto":
    case "pb_if":
    case "pb_implements":
    case "pb_import":
    case "pb_in":
    case "pb_instanceof":
    case "pb_int":
    case "pb_interface":
    case "pb_long":
    case "pb_native":
    case "pb_new":
    case "pb_null":
    case "pb_package":
    case "pb_private":
    case "pb_protected":
    case "pb_public":
    case "pb_return":
    case "pb_short":
    case "pb_static":
    case "pb_super":
    case "pb_switch":
    case "pb_synchronized":
    case "pb_this":
    case "pb_throw":
    case "pb_throws":
    case "pb_transient":
    case "pb_try":
    case "pb_typeof":
    case "pb_var":
    case "pb_void":
    case "pb_volatile":
    case "pb_while":
    case "pb_with":
      key = key.substr(3);
      break;
  }
  const upperKey = key.charAt(0).toUpperCase() + key.substr(1);
  return `set${upperKey}`;
}

@MarcusLongmuir WDYT? Usage is a little clunky as you need to provide both generic types (although my TS is weak, can you express this better?)

const book = fromObject<Book, Book.AsObject>(Book, {
  title: "Hello",
  author: "Dave",
  isbn: 1234,
});