Proper class format in modern ES

Is the following an acceptable way to initialize a class?

class Person {
    name = undefined; // or just `name` ?
    age = undefined; // or just `age` ?
    constructor(name, age) {
        Object.assign(this, {name, age});
    }
}
let p = new Person('tom', 10);

By that I mean, more specifically,

• Is Object.assign(this, {...variables}) a good way to do all the this assignments?
• Is it considered good practice to stick the variables at the top, or should they be placed within the constructor?
• Is it better to explicitly set a variable to undefined or not? That is, is name = undefined; or name; preferable?