Creating a mapped union type from nested objects based on object keys can be achieved by following these steps

I am currently attempting to generate a custom type based on a design token JSON file.

The JSON data is structured as follows:

{
    "Black": {
        "4": { "value": "#f6f6f6" },
        "6": { "value": "#f2f2f2" },
        "10": { "value": "#e8e8e8" },
        "20": { "value": "#d3d3d3" },
        "30": { "value": "#bcbcbc" },
        "40": { "value": "#a7a7a7" },
        "50": { "value": "#909090" },
        "60": { "value": "#7b7b7b" },
        "70": { "value": "#646464" },
        "80": { "value": "#4e4e4e" },
        "90": { "value": "#383838" },
        "100": { "value": "#222222" }
    },
    "Blue": {
        "4": { "value": "#F5F8F8" },
        "8": { "value": "#EBF0F1" },
        "10": { "value": "#E5EBED" },
        "20": { "value": "#CCD9DC" },
        "30": { "value": "#B2C5CA" },
        "40": { "value": "#99B3B9" },
        "50": { "value": "#7F9FA7" },
        "60": { "value": "#668C96" },
        "70": { "value": "#4C7984" },
        "80": { "value": "#336673" },
        "100": { "value": "#004050" }
    },
    "Teal": {
        "20": { "value": "#ccfbf0" },
        "40": { "value": "#99f8e1" },
        "60": { "value": "#66f4d3" },
        "80": { "value": "#33f1c4" },
        "100": { "value": "#00edb5" }
    }
}

Currently, I have created a union type for the colors using 

type Color = keyof typeof colorJSON;

My next task is to establish another union type for all the nested keys within each color object that represent different tint levels like 

type Tint = '4' | '6' | '8' etc...
. However, I'm struggling to recursively iterate through the colors and access these keys.

---Edit---

My goal is to ensure that the type automatically updates if new colors are added to the JSON file, so it needs to iterate through the structure rather than directly reference color names.

typescriptunion-typesmapped-types

Answer №1

Take a look at this illustration:

const colorJSON = {
  "Black": {
    "4": { "value": "#f6f6f6" },
    "6": { "value": "#f2f2f2" },
    "10": { "value": "#e8e8e8" },
    "20": { "value": "#d3d3d3" },
    "30": { "value": "#bcbcbc" },
    "40": { "value": "#a7a7a7" },
    "50": { "value": "#909090" },
    "60": { "value": "#7b7b7b" },
    "70": { "value": "#646464" },
    "80": { "value": "#4e4e4e" },
    "90": { "value": "#383838" },
    "100": { "value": "#222222" }
  },
  "Blue": {
    "4": { "value": "#F5F8F8" },
    "8": { "value": "#EBF0F1" },
    "10": { "value": "#E5EBED" },
    "20": { "value": "#CCD9DC" },
    "30": { "value": "#B2C5CA" },
    "40": { "value": "#99B3B9" },
    "50": { "value": "#7F9FA7" },
    "60": { "value": "#668C96" },
    "70": { "value": "#4C7984" },
    "80": { "value": "#336673" },
    "100": { "value": "#004050" }
  },
  "Teal": {
    "20": { "value": "#ccfbf0" },
    "40": { "value": "#99f8e1" },
    &...
(type ColorMap<T extends Record<string, Record<string, unknown>>>)

ColorMap - scans through json keys (Black/Blue/Teal) to get the union of keys of nested objects.

Values - provides the union of all object values.

The composition of ColorMap and Values yields the union of all keys of nested objects since object values are unions of keyof json nested objects.

P.S. Recursive iteration through this object type might not be necessary. However, if you want recursive solutions, refer to my article

Answer №2

To access the nested object's type, you can utilize bracket notation along with the keyof method to switch between different colors:

type ColorJSON = typeof colorJSON;
type Color = keyof ColorJSON;
type Shade = keyof ColorJSON['Black'] | keyof ColorJSON['Blue'] | keyof ColorJSON['Teal']

In this specific scenario, it is not necessary to include Teal as its keys are already included in Blue.

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