Using Closure to Protect Properties Within an Object from Being Modified Externally

• In the previous post, bird had a public property name. It is considered public because it can be accessed and changed outside of bird's definition.

bird.name = "Duffy";

• Therefore, any part of your code can easily change the name of bird to any value. Think about things like passwords and bank accounts being easily changeable by any part of your codebase. That could cause a lot of issues.

• The simplest way to make this public property private is by creating a variable within the constructor function. This changes the scope of that variable to be within the constructor function versus available globally. This way, the variable can only be accessed and changed by methods also within the constructor function.
  

function Bird() {
  let weight = 15;

  this.getWeight = function() {
    return weight;
  }
}
let ducky = new Bird();
console.log(ducky.getWeight()); // will display 15

• Here getWeight is a privileged method, because it has access to the private variable weight. This is possible because weight is declared in the same context as getWeight. In JavaScript, a function always has access to the context in which it was created. This is called closure.