How can I convert an object to JSON using JSON.stringify and ensure its type is recognized as JSON?

When I attempt the following code snippet:

import { MyType } from 'somewhere';

class MyClass {
    myObj: MyType = new MyType();

    updateObject(newVal: string): void {
        myObj.thing = newVal;
        this.saveStuff(JSON.stringify(myObj));
    }

    saveStuff(json: JSON): void {
        // http request...
    }
}

I encounter an error indicating that I am passing a string instead of JSON, despite being aware that it is actually a string. How can I adjust it to treat the string as JSON?

I experimented with attempting to cast the string as JSON like so: JSON.stringify(foo) as JSON or <JSON> JSON.stringify(foo). However, in both cases, I receive an error stating "Type 'string' cannot be converted to type 'JSON'."

Answer №1

JSON is not a data type. When you use JSON.parse(str) to parse a string, the result is an object literal.

When you call JSON.stringify(foo) in your code, you are converting the object literal foo to a string.

As a result, your function saveStuff() ends up receiving a string input.

The acronym JSON stands for JavaScript Object Notation, which serves as a standard for representing objects.

Answer №2

When using TypeScript type annotations, you are indicating the type you anticipate a value to be (not declaring it). Often, you may set a type annotation only to find out during runtime that the actual type is different.

However, in some cases, the TS compiler can predict types in advance. For instance, when calling JSON.stringify, the compiler knows it returns a string. If you have specified that the saveStuff method should accept a JSON object, the compiler will catch any type mismatches.

Despite its content, a string remains as such, whether it holds JSON data, XML, or poetry. The JSON class serves as a tool for serializing and deserializing JavaScript objects into and from strings with JSON formatting.

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