What is an object?

An object is a data structure that holds related variables.

Object Syntax

An object is declared like any other variable. The object wraps related variables in curly braces {}.

Instead of declaring variables in an object with let variableName = 'some data', the variables in an object use a colon to separate the variable and the data variableName: 'some data'. The variable is called the key and the data is called the value - together they are a key-value pair.

Below is an object with the variable name aPersonObject and three key-value pairs.

let aPersonObject = {
    name: 'Andrea',
    age: 39,
    country: 'USA'
}

Accessing and Changing an Object

Accessing a value

There are two ways to access an object value.

One way is to type the key inside of quotes and a bracket after the object name. Note we use quotes because the keys are strings when created in the way you have learned.

let aPersonObject = {
    name: 'Andrea',
    age: 39,
    country: 'USA'
}
console.log(aPersonObject['name']); // prints 'Andrea'

The second way is type the key after the object name and a period.

let aPersonObject = {
    name: 'Andrea',
    age: 39,
    country: 'USA'
}
console.log(aPersonObject.name); // prints 'Andrea'

Changing or Adding to an Object

To change or add a key-value pair to an object you use the same syntax you used to access a value then you assign it to a value.

let aPersonObject = {
    name: 'Andrea',
    age: 39,
    country: 'USA'
}
console.log(aPersonObject); // {name: "Andrea", age: 39, country: "USA"}
// adding a new key-value pair
aPersonObject.city = 'San Francisco'; 
console.log(aPersonObject); // {name: "Andrea", age: 39, country: "USA", city: "San Francisco"}
// changing an old key-value pair
aPersonObject.name = 'Ravi';
console.log(aPersonObject); // {name: "Ravi", age: 39, country: "USA", city: "San Francisco"}

Methods

Object.keys(x)

The Object.keys(x) method takes the object as a parameter and returns a new array with the keys as array items.

let aPersonObject = {
    name: 'Andrea',
    age: 39,
    country: 'USA'
}
let aPersonArrayWithKeys = Object.keys(aPersonObject);
console.log(aPersonArrayWithKeys); // ["name", "age", "country"]

Object.values(x)

The Object.values(x) method takes the object as a parameter and returns a new array with the values as array items.

let aPersonObject = {
    name: 'Andrea',
    age: 39,
    country: 'USA'
}
let aPersonArrayWithValues = Object.values(aPersonObject);
console.log(aPersonArrayWithValues); // ["Andrea", 39, "USA"]