Question 1: How can we prevent JSON.parse() from automatically converting a single string value to a number?
JSON is primarily a text format, so when using JSON.parse(x), the input x must be a string. However, JSON data can represent values of various types, not just strings. It seems like there may be confusion between the actual value and its representation, which could lead to unexpected conversions.
If you convert the number 12345 to JSON (JSON.stringify(12345)), you will get the string "12345". If you then parse this string (JSON.parse("12345")), you will retrieve the number 12345. To maintain the string value, you need to properly encode it as JSON by using JSON.stringify("12345"), resulting in "\"12345\"". Parsing this encoded string (JSON.parse('"12345"')) will return the original string "12345".
In essence, to avoid JSON.parse() converting a single string value into a number, ensure that the value is correctly quoted. If the intention is to handle the input string as-is without conversion, simply use it directly without invoking JSON.parse().
If these solutions do not address your specific scenario, please provide more details about your issue following the guidelines for creating a Minimal, Complete, and Verifiable example.
Question 2: How can we verify that the object returned after JSON parsing matches the predefined generic type?
In TypeScript, the type system operates during design time and gets erased when the code is executed in JavaScript. This means that runtime access to interfaces and type parameters like TResponse is unavailable. The recommended approach is to develop runtime logic first (as would be done in pure JavaScript) and utilize inference techniques to establish correct types during design time.
The IApiCall interface does not structurally depend on TResponse, which is discouraged due to possible ambiguity. Even if runtime code is well-defined and type inference is attempted, the compiler will struggle to deduce TResponse's identity.
A suggested solution involves modifying the IApiCall interface to incorporate a member that serves as a type guard function. Subsequently, custom runtime tests for each target type need to be devised.
For instance:
interface Person {
name: string,
age: number;
}
const personApiCall: IApiCall<Person> = {
method: "GET",
url: "https://example.com/personGrabber",
validate(x): x is Person {
return (typeof x === "object") &&
("name" in x) && (typeof x.name === "string") &&
("age" in x) && (typeof x.age === "number");
}
}
The validation function within personApiCall performs a check to verify if the object complies with the Person interface. Consequently, the general function call() can be tailored as follows:
const call = <TResponse>(api: IApiCall<TResponse>): Promise<TResponse | undefined> => {
return fetch(api.url, { method: api.method }).
then(r => r.json()).
then(data => api.validate(data) ? data : undefined);
};
This structure enables automatic recognition of the asynchronous result's type by the compiler. For example:
async function doPersonStuff() {
const person = await call(personApiCall); // no explicit type needed
if (person) {
console.log(person.name);
console.log(person.age);
} else {
console.log("Notify missing Person information!")
}
}
I trust these insights guide you towards resolving your queries effectively. Best of luck!