Encapsulate Variable

Goal

All reads and writes pass through a small named function that owns validation, logging, and invariants.

Before the refactoring

let defaultOwner = { firstName: 'Martin', lastName: 'Fowler' };

After the refactoring

let _defaultOwner = { firstName: 'Martin', lastName: 'Fowler' };
function defaultOwner() { return _defaultOwner; }
function setDefaultOwner(o) { _defaultOwner = o; }

Savings

A bug fix or audit becomes a one-line addition inside the wrapper; consumers never need to change.

Note

Adds a layer of indirection that pays off only when every access goes through the wrapper — leakage of direct access undoes the benefit.