Is there a tool or resource available that allows you to input an object and receive a TypeScript type or interface representation of that object?

Throughout this year, I've been diving into the world of React and TypeScript. One thing that stood out to me is how challenging it can be to type complex objects. It got me thinking - wouldn't it be great if there was a way or a helper function that could take an object as input and return a TypeScript interface or type for us to use in our code?

For instance, consider the following object:

const complexObject = {
    "hsl": {
        "h": 118.48101265822783,
        "s": 1,
        "l": 0.5,
        "a": 1
    },
    "hex": "#06ff00",
    "rgb": {
        "r": 6,
        "g": 255,
        "b": 0,
        "a": 1
    },
    "hsv": {
        "h": 118.48101265822783,
        "s": 1,
        "v": 1,
        "a": 1
    },
    "oldHue": 118.48101265822784
}

Typing this object manually can indeed be quite daunting, especially for beginners like myself. But imagine if we had a library where we could simply call a function like getType. We could then do something like this:

getType(complexObject); 

// returns 
type complexObject = {
    hex: string;
    hsl: { h: number; s: number; l: number; a: number };
    hsv: { h: number; s: number; v: number; a: number };
    rgb: { r: number; g: number; b: number; a: number };
};

Answer №1

If you simply wish to utilize a type within a file like how getType is demonstrated above, you can use typeof, as exemplified in Ozan's response. While typeof functions at runtime to provide a string output in regular JavaScript, TypeScript assigns extra significance to typeof: it enables you to leverage the type of an existing identifier in a type expression.

// Executed in the generated JavaScript.
const someValue = typeof complexObject; // "object"

// Type only: not included in JavaScript output.
type SomeType = typeof complexObject; // { hsl: { ... }, ... }

// Also type only, since it follows the : and TS interprets it as a type.
const typedValue: typeof complexObject = getComplexObject();
//    field name: type expression      = initial value

Keep in mind that types do not exist during runtime, so there is no possibility of actually returning a type as a runtime value or function return statement similar to getType. A function such as getType may yield a value, and that value could have a valuable type associated with it, but it is impossible to return the type itself using a function.

On a side note: if your objective is to create a declaration file based on existing JavaScript code, or if you intend to access the interface definition for the purpose of copying it into your own code, a common tool for achieving this is dts-gen.

Answer №2

Forget about using a function called getType to fetch the type and reuse it later in your code.

All you have to do is utilize the typeof operator and store that result in a variable named type.

let dataType = typeof data;

From now on, you can employ dataType as a type for other variables within your project.

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