What are getters and setters for?

They let a property be backed by a function while still being read and written like an ordinary property.

const user = {
  firstName: "Mai",
  lastName: "Tran",

  get fullName() {
    return `${this.firstName} ${this.lastName}`;
  },

  set fullName(value) {
    [this.firstName, this.lastName] = value.split(" ");
  },
};

user.fullName;              // "Mai Tran" — no parentheses
user.fullName = "Nam Le";   // runs the setter

What they are good for

• Computed values that should look like data: fullName, area, isExpired.
• Validation on assignment, so an invalid value can never be stored.
• Keeping an API stable when a plain property later needs logic behind it — callers do not change.
• Lazy computation, calculating on first read and caching.

class Rectangle {
  #width = 0;
  get width() { return this.#width; }
  set width(v) {
    if (v < 0) throw new RangeError("width must be positive");
    this.#width = v;
  }
}

Pair them with a private #field rather than the old _name convention, which is only a hint.

Things to watch

A getter must not be expensive or have side effects. Readers expect obj.x to be cheap, and a getter that fetches data or mutates state surprises everyone — including the debugger, which evaluates getters when you expand an object.

A getter without a setter makes the property silently read-only in sloppy mode; assignment throws in strict mode and modules.

And infinite recursion is easy to write: inside get name, referring to this.name calls the getter again. Back it with a differently named field.

When a method is better

If the operation is slow, takes arguments, or clearly does something, make it a method. user.getFullName() sets the right expectation; user.fullName should feel like reading a value.