validate a json object against a typescript interface in typescript

One way to validate a JSON object against a TypeScript interface is to use a library called Ajv, which is a JSON schema validator.

First, you'll need to install the Ajv package:

index.ts
npm install ajv
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Next, define your TypeScript interface as you normally would, but with an additional __brand property:

index.ts
interface Person {
  __brand: 'Person';
  name: string;
  age: number;
}
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The __brand property is used to create a unique, nominal type that can be used to distinguish the interface from other objects.

Then, define a JSON schema that corresponds to your TypeScript interface, using the type and properties keywords:

{
  "type": "object",
  "properties": {
    "name": { "type": "string" },
    "age": { "type": "number" }
  },
  "required": ["name", "age"],
  "additionalProperties": false
}
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This schema specifies that the JSON object should be an object with name and age properties that are strings and numbers respectively.

Finally, load the Ajv library and create a new instance, passing in the JSON schema:

index.ts
import Ajv from 'ajv';

const ajv = new Ajv();
const validate = ajv.compile(schema);
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You can then use the validate function to check if a JSON object matches your TypeScript interface:

index.ts
const person: unknown = {
  name: "John Doe",
  age: 30
};

if (validate(person) && (<Person>person).__brand === "Person") {
  // `person` is a valid `Person` object
} else {
  // `person` is not a valid `Person` object
}
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The validate function returns a boolean that indicates whether the input JSON object matches the schema. The second condition checks that the __brand property matches the expected value, ensuring that the JSON object is also a valid instance of your TypeScript interface.