A succint funtion that transforms JS Object to using a declarative schema

transform.js

// Code

export const pickDeep = (obj: Dict<any>, key: string) =>
  hasKey(obj, key) ? obj[key] : key.split(".").reduce((o, k) => o?.[k], obj);

export const transform = (from: Dict<any>, to: Dict<any>) =>
  keys(to).reduce((o: Dict<any>, k) => {
    const t = to[k]; // for each key that we want in the new object, get the transformer
    o[k] = Array.isArray(t) // check if the transformer is an array
      ? typeof last(t) === "object" // if so, check if the last element of the transformer array is another 'to' object
        ? pickDeep(from, t[0]).map((i: Dict<any>) => transform(i, last(t))) // if so, apply this 'to' transformation to the array pointed in the first element of the transformer array
        : last(t)(...t.slice(0, -1).map((u) => pickDeep(from, u))) // otherwise last element must be a function, pass it the values pointed in the transformer array
      : isObject(t) // if transformer is another object
      ? transform(from, t) // recursively apply transform
      : typeof t === "string" // if its a string
      ? pickDeep(from, t) // pick the deep value
      : t; // otherwise just store the passed value as it is in the transformed object

    return o;
  }, {});


// Usage

const source = {
  user: {
    id: 1,
    first_name: "Ali",
    last_name: "Azhar",
    role: {
      id: 1,
      title: "Software Engineer",
    },
  },
};

const transformer = {
  user: {
    // combine multiple values from source object
    name: ["user.first_name", "user.last_name", (firstName: string, lastName: string) => `${firstName} ${lastName}`],
  },
  role: "role.title",
};

// Another example

{
  id: "id",
  text: "question.text",
  shortText: "question.text_short",
  options: [
    "available_options", // transformation schema for an item within the list `available_options`
    {
      id: "id",
      text: "text",
      subOptions: [
        "sub_options", // transformation schema for an item within the list `sub_options`
        {
          id: "id",
          text: "text",
          subOptions: "sub_options",
        },
      ],
    },
  ],
}