angular - How to parse a JSON object to a TypeScript Object

Question

I am currently trying to convert my received JSON Object into a TypeScript class with the same attributes and I cannot get it to work. What am I doing wrong?

Employee Class

export class Employee{
    firstname: string;
    lastname: string;
    birthdate: Date;
    maxWorkHours: number;
    department: string;
    permissions: string;
    typeOfEmployee: string;
    note: string;
    lastUpdate: Date;
}

Employee String

{
    "department": "<anystring>",
    "typeOfEmployee": "<anystring>",
    "firstname": "<anystring>",
    "lastname": "<anystring>",
    "birthdate": "<anydate>",
    "maxWorkHours": <anynumber>,
    "username": "<anystring>",
    "permissions": "<anystring>",
    "lastUpdate": "<anydate>"
    //I will add note later
}

My Attempt

let e: Employee = new Employee();

Object.assign(e, {
    "department": "<anystring>",
    "typeOfEmployee": "<anystring>",
    "firstname": "<anystring>",
    "lastname": "<anystring>",
    "birthdate": "<anydate>",
    "maxWorkHours": 3,
    "username": "<anystring>",
    "permissions": "<anystring>",
    "lastUpdate": "<anydate>"
});

console.log(e);

Link to Typescript Playground

Answer 1

If you use a TypeScript interface instead of a class, things are simpler:

export interface Employee {
    typeOfEmployee_id: number;
    department_id: number;
    permissions_id: number;
    maxWorkHours: number;
    employee_id: number;
    firstname: string;
    lastname: string;
    username: string;
    birthdate: Date;
    lastUpdate: Date;
}

let jsonObj: any = JSON.parse(employeeString); // string to generic object first
let employee: Employee = <Employee>jsonObj;

If you want a class, however, simple casting won't work. For example:

class Foo {
    name: string;
    public pump() { }
}

let jsonObj: any = JSON.parse('{ "name":"hello" }');
let fObj: Foo = <Foo>jsonObj;
fObj.pump(); // crash, method is undefined!

For a class, you'll have to write a constructor which accepts a JSON string/object and then iterate through the properties to assign each member manually, like this:

class Foo {
    name: string;

    constructor(jsonStr: string) {
        let jsonObj: any = JSON.parse(jsonStr);
        for (let prop in jsonObj) {
            this[prop] = jsonObj[prop];
        }
    }
}

let fObj: Foo = new Foo(theJsonString);