Change output names in API return object - node.js

Question

I am very new to nodejs and typescript.
I have try to provide an API via express.
I have try to return a custom object on my API who looks like that :
export class Auction {
private _currentPrice:number = 0;
private _auctionName:string;
public constructor(currentPrice: number , auctionName: string) {
this._currentPrice = currentPrice;
this._auctionName = auctionName;
}
/**
* Getter auctionName
* #return {string}
*/
public get auctionName(): string {
return this._auctionName;
}
/**
* Setter auctionName
* #param {string} value
*/
public set auctionName(value: string) {
this._auctionName = value;
}
/**
* Setter currentPrice
* #param {number } value
*/
public set currentPrice(value: number ) {
this._currentPrice = value;
}
/**
* Getter currentPrice
* #return {number }
*/
public get currentPrice(): number {
return this._currentPrice;
}
}
But what I have seen is that the answer of my API is something like :
{"_currentPrice":0,"_auctionName":"toto"}
I was expecting something like
{"currentPrice":0,"auctionName":"toto"}
Is there any way to automaticaly convert it to the format I want ?

Answer 1

This is happening because when the TypeScript is compiled to JavaScript, objects created by that class have public _currentPrice and _auctionName properties (because TypeScript "private" properties are only private in terms of TypeScript's type system) and they don't have their own currentPrice and auctionName properties (they inherit them from their prototype, which has them as accessor properties). JSON.stringify only includes "own" properties.
You can deal with it in a few ways:
By using simple properties for currentPrice and auctionName. You have public accessors for both get and set for both properties, so there doesn't seem to be any reason to use private properties to hold their values. Or,
By providing your own toJSON method for the class:
toJSON() {
return {currentPrice: this._currentPrice, auctionName: this._auctionName};
}
Despite the name "toJSON", this method isn't supposed to return JSON; it's supposed to return the value for the object that should be converted to JSON. So in this case, you return an object with the properties you want the returned JSON to have.
A third solution would be to use JavaScript's own private properties (they're supported in up-to-date Node.js versions) and "own" accessors for them on the objects, but I don't think TypeScript supports JavaScript's private properties yet.