TypeScript construct class with json

Question

I am building a sample project with Angular2/Typescript in order to use it as a new frontend for an existing backend code.

I really like the ability to create types and consider to use some of the JSON objects served by the backend as typed classes like this:

module DomainObjects {
  export class SomeDomainObject {
    constructor(attr1:string, attr2:number) {...}
    ...
  }
}

Some of the JSON code that is returned by the backend is very large, so I don't want to work with a huge amount of parameters in the constructor. At best i just pass a JSON object as a single parameter to the constructor which does some checks (or not). On the other hand I'd like to access the JSON object directly. Is something like this possible:

myobject:SomeDomainObject;
...
this.myobject = new SomeDomainObject({id:10,color:'green'});

and access myobject in a template like this

{{myobject.color}}

without having another reference like {{myobject.json.color}}

Matthias247 · Accepted Answer · 2016-04-28 20:42:57Z

1

You can model your JSON data with interfaces (instead of classes). Then you can simply assign the received JSON to it (instead of calling a constructor).

For validation you will most likely need to build a validation function that checks if the received JSONs structure really equals the type that you described in your interface. You could also build a validate and assign function with a signature like

function toTypedData(input: any):SomeDomainObject { ... }

You can also use JSON schema and a suitable validation library to perform that step.

answered Apr 28, 2016 at 20:42

Matthias247

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2 Comments

Jan B. Over a year ago

Thank you. I think that pretty much solves the issue. Coming from the Java world, I had a slightly different notion of what interfaces are for.

John Weisz Over a year ago

@user3802631 The only single issue with using interfaces is that if your JSON represents objects that have methods (eg.: if your SomeDomainObject had a method), those methods won't exist on objects you think they exist.

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