To determine if two constant objects share identical structures in TypeScript, you can compare their properties

There are two theme objects available:

const lightMode = {
  background: "white",
  text: {
    primary: "dark",
    secondary: "darkgrey"
  },
} as const

const darkMode = {
  background: "black",
  text: {
    primary: "white",
  },
} as const

If the structure of the default theme object (lightMode) does not match that of the darkMode object, I want to receive a type error.

This serves as a reminder for individuals to update the darkMode object with new color values when they make changes to the lightMode object's colors.

Answer №1

Stop overcomplicating things.

It's crucial to establish a type that both objects must adhere to for accuracy. In Typescript, creating solid data types from the start will benefit you in the long haul.

Define a type like this:

type UITheme = {
    background: string,
    text: {
        primary: string
        secondary: string
    }
}

Ensure that your objects are constructed correctly using this type.

const lightMode: UITheme = {
  background: "white",
  text: {
    primary: "dark",
    secondary: "darkgrey"
  },
} as const

const darkMode: UITheme = {
  background: "black",
  text: {
    primary: "white",
  },
} as const
// Type error since 'secondary' property is missing in object 
//   '{ readonly primary: "white"; }'
// which is required based on type
//   '{ primary: string; secondary: string; }'.

View playground


If you require the inference of string literal types, utilize a generic function to create and enforce the objects.

type UITheme = {
    background: string,
    text: {
        primary: string
        secondary: string
    }
}

const createUIMode = <T extends UITheme>(theme: T) => theme

const lightMode = createUIMode({
  background: "white",
  text: {
    primary: "dark",
    secondary: "darkgrey"
  },
} as const)

const darkMode = createUIMode({
  background: "black",
  text: {
    primary: "white",
  },
} as const)
// error

View playground

Answer №2

Take a look at my initial try:

interface CreateNormalizedTheme<T extends object> {
  themeObject: T;
}

const exampleConstant: CreateNormalizedTheme<typeof primaryTheme> =
  secondaryTheme as CreateNormalizedTheme<typeof secondaryTheme>;

Initially, the type errors may seem overwhelming, but a closer examination reveals that one of our themes is missing a key property from the other!

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