How to parse a JSON object to a TypeScript Object

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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 = JSON.parse(employeeString); // string to "any" object first
let employee = jsonObj as Employee;

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

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

let jsonObj = JSON.parse('{ "name":"hello" }');
let fObj = jsonObj as Foo;
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 = JSON.parse(jsonStr);
        for (let prop in jsonObj) {
            this[prop] = jsonObj[prop];
        }
    }
}

let fObj = new Foo(theJsonString);

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