objects

Objects

Let’s say you are trying to represent a person using code. What kind of attributes do you think are important to store about a person? How would you store these attributes using what you know so far? Perhaps we'd try something like this:

const firstName = 'Nicolas'
const lastName = 'Marcora'
const age = 33

Mmm, ok. What if we want to have a second person?

const firstName1 = 'Nicolas'
const lastName1 = 'Marcora'
const age1 = 33

const firstName2 = 'Sergio'
const lastName2 = 'Neves'
const age2 = 30

How could we make this better? The answer is Objects. JavaScript objects are a data type that consists of keys and values, wrapped with curly braces. We can use objects to collect together related properties that represent a single instance of something, like a person:

const person = {
  firstName: 'Nicolas',
  lastName: 'Marcora',
  age: 33
}

Objects are composed of Key value pairs, separated by a colon (:). In the example above, there are 3 key value pairs:

1. The key firstName with a value of Nicolas
2. The key lastName with a value of Marcona
3. The key age with a value of 33.

Keys are always strings, but values can be any valid JavaScript datatype: number, string, booleans, null, undefined, array and even object.

👨‍💻 Run these examples in your REPL as you read along! 👨‍💻

Let's look at how we can add keys to an object. Starting with a blank object:

const instructor = {}

We can add a new key using the object[key] syntax:

instructor['firstName'] = 'Nicolas'
>>> { firstName: 'Nicolas' }

And, if you don’t have any special characters, this cleaner syntax (also know as dot notation) does the same thing:

instructor.lastName = 'Marcora'
>>> { firstName: 'Nicolas', lastName: 'Marcora' }

Similarly, we can read keys from an object using the same syntax. First using object[key]:

instructor['firstName']
>>> 'Nicolas'

...and using dot syntax:

instructor.lastName
>>> 'Marcora'

Key values can also be updated in the same way:

instructor['firstName'] = 'Sergio'
instructor
>>> { firstName: 'Sergio', lastName: 'Marcora' }

And the dot notation equivalent:

instructor.lastName = instructor.lastName.toUpperCase()
instructor
>>> { firstName: 'Sergio', lastName: 'MARCORA' }

Finally, to delete keys from an Object, you can use the delete keyword:

delete instructor.lastName
instructor
>>> { firstName: 'Sergio' }

Next

Work your way through the tests for this section. You can use the references below and also the example.js file to see more code samples. Remember you can make use of the Node REPL to try out and experiment with code.

References

• Boolean Objects Slides
• MDN Objects