Object properties tutorial

properties.js

function Person(firstName, lastName, age, ssn) {
  // Declaring this way by default will make your property
  // readable, writable, and enumerable
  this.firstName = firstName;
  this.lastName = lastName;

  // Let's make a getter-only method that returns the
  // two values as a whole name
  Object.defineProperty(this, 'fullName', {
    get: function() {
      return this.firstName + ' ' + this.lastName;
    },
    enumerable: false, // We don't want this to appear in for..in loops
  });

  // Let's make a getter-setter method to serialize data.
  // In this case, we want "age" to always be a number, even
  // if the number is a string, and throw an error if it's not
  // parseable
  var _age = age; // private member scoped to this function
  Object.defineProperty(this, 'age', {
    set: function(val) {
      var v = +val; // convert val to a number
      if (Number.isNaN(v)) {
        throw new RangeError('age must be a number');
      }
      _age = v;
    },
    get: function() {
      return _age;
    },
    enumerable: true, // Display this property in for..in loops
  });

  // Finally, we'll make a read-only field
  Object.defineProperty(this, 'ssn', {
    enumerable: true,
    readable: true,
    writable: false,
    value: ssn,
  });
}

// Let's create an instance of our new class
var me = new Person('Sean', 'Spradlin', 31, '123-45-6789');

// Now we'll do a for..in loop to check the values
console.log('Displaying keys...');
Object.keys(me).forEach(function(key) {
  console.log(key, ':', me[key]);
});

// Let's get the full name
console.log('\nGetting full name...');
console.log(me.fullName);

// Enumerable helps with JSON stringify as well
console.log('\nDisplaying JSON...')
console.log(JSON.stringify(me));

// Setting age as a string will convert it to a number
console.log('\nTesting age...');
me.age = '25'; // string
console.log(typeof me.age, me.age); // number

// Let's try to set it as a non-number string
console.log('\nSetting age as not a number...');
try {
  me.age = 'Hello world';
} catch (error) {
  console.log('Oops!', error.message);
}

// Now let's try to change our SSN
console.log('\nAttempting to change SSN...');
me.ssn = '555-55-5555';
console.log(me.ssn);