Given the following classes
class A {
constructor(){
this.name ="Some name";
}
name:string;
}
class C extends A {
get Age() {
return 21;
}
SayHello(){
return "Hello";
}
}
If you would to build the OBJECT from a JSON Parse
var demo2:C= JSON.parse('{"name":"Joan of Arc"}') AS C;
This will not work:
console.log(demo2.Age);
console.log(demo2.SayHello());
Any workaround or ideas?
It doesn't work because Typescript doesn't cast JS objects, meaning that it doesn't change or modify them, it's only used for types. So when you use as statement, demo2 is being treated by Typescript as instance of C, while in reality demo2 isn't instance of C.
To make it work you can modify C so it has a constructor which accepts an object and assigns its properties to this
// add this to the body of C
constructor(obj: C) {
Object.assign(this, obj);
}
// later in code
const demo2 = new C(JSON.parse('{"name":"Joan of Arc"}') AS C);
JSON.parse(...) as AnyClass will not (cast) or create the object AnyClass.
One clever solution are:
const parsedJson = JSON.parse(...)
const myObj = new AnyClass();
Object.assign(myObj, parsedJson);
myObj. Consider this. You can easily malform your object and the compiler will let you shoot yourself in the foot.
as(or<>syntax) is a type assertion. You just override the compiler and tell it "regardless of what you think this thing is, not consider it this other thing. Just trust me". That doesn't actually change anything about the object, simply stops compilation errors, not runtime ones. So, if you have object of one shape and want it in another, you have to change it yourself. With classes the usual way is to accept an object in the constructor or otherwise initialise the class instance via an object.