Objects and Data Structures

Use getters and setters

Using getters and setters to access data on objects could be better than simply
looking for a property on an object. “Why?” you might ask. Well, here’s an
unorganized list of reasons why:

• When you want to do more beyond getting an object property, you don’t have
  to look up and change every accessor in your codebase.
• Makes adding validation simple when doing a set.
• Encapsulates the internal representation.
• Easy to add logging and error handling when getting and setting.
• You can lazy load your object’s properties, let’s say getting it from a
  server.

Bad:

function makeBankAccount() {
  // ...
  return {
    balance: 0,
    // ...
  };
}
const account = makeBankAccount();
account.balance = 100;

Good:

function makeBankAccount() {
  // this one is private
  let balance = 0;
  // a "getter", made public via the returned object below
  function getBalance() {
    return balance;
  }
  // a "setter", made public via the returned object below
  function setBalance(amount) {
    // ... validate before updating the balance
    balance = amount;
  }
  return {
    // ...
    getBalance,
    setBalance,
  };
}
const account = makeBankAccount();
account.setBalance(100);

Make objects have private members

This can be accomplished through closures (for ES5 and below).

Bad:

const Employee = function(name) {
  this.name = name;
};
Employee.prototype.getName = function getName() {
  return this.name;
};
const employee = new Employee('John Doe');
console.log(`Employee name: ${employee.getName()}`); // Employee name: John Doe
delete employee.name;
console.log(`Employee name: ${employee.getName()}`); // Employee name: undefined

Good:

function makeEmployee(name) {
  return {
    getName() {
      return name;
    },
  };
}
const employee = makeEmployee('John Doe');
console.log(`Employee name: ${employee.getName()}`); // Employee name: John Doe
delete employee.name;
console.log(`Employee name: ${employee.getName()}`); // Employee name: John Doe