Comment by ubertaco

An approach I've seen is to have each class extend from some abstract base class (I know, OO blech) that looks like this:

    abstract class AbstractClassObject {
        constructor(json?: any){
            if (json){
                this.updateFromJSON(json)
            }
        }
        public updateFromJSON = (json: any): this => {
            Object.assign(this, json);
            return this;
        }
    }

That gives you the "magic" just by extending the base, while also allowing custom behavior for a given class (by overriding updateFromJSON).