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The Quite Nice and Fairly Accurate Intro to JavaScript Objects (pt. 2)

ale3oula profile image Alexandra ・3 min read

JavaScript has two data types: Primitives, and objects. I made an article with an introduction in JavaScript Primitives in The Quite Nice and Fairly Accurate Introduction to JavaScript Primitive Data Types.

So, let's now see the Objects basics. 😎

The objects

In JavaScript or general in programming, objects can model real-world things, e.g. an animal, a car or a human. Objects are used to store key-value collections and represent more complex entities.

We can define (and create) a JavaScript object with an object literal by using curly braces, {}:

Empty Object

Key: value

We can fill an object with unordered data, called properties. A property is a key: value pair, where a key is a string (also property name), and value can be of any data type. A key is similar to a variable name that points to a location in memory that holds a value. The value can be any data type (including functions or other objects).

Object with properties

Accessing the Properties

There are two ways to access the object properties: Dot notation and Bracket Notation.

With the dot notation, we write the object’s name, the dot operator and then the property name:

Dot notation

With the bracket notation, we pass in the property name (key) as a string:

Bracket notation

Assign to a property

Objects are mutable, which means that we can update them. We can use dot or bracket notation to select the property and with the help of the assignment operator, we can add new key-value pairs (if there was no property with that name) or change an existing property (if the property already exists). We can also delete a property from the object with the delete operator.

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Methods as Properties

We can also include methods in our object literals; With the ES6 syntax we can include them in the object as:

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*Pass by what? *

In JS when a function is called, it directly passing the value of the variable as the argument. Changing the variable inside the function doesn’t affect the variable passed. However, objects are passed by reference. When we pass a variable assigned to an object into a function, this is interpreted as pointing to the space in memory holding that object. As a result, functions can change this object permanently.

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Iterating through Objects

JavaScript provides us with the for...in statement to iterate through the properties of an object.

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References:

Objects
JavaScript Objects
Working with Objects
4 ways to create an Object in JS (with examples)

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Alexandra

@ale3oula

Digital maiden - Front end Engineer

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Nice introduction Alexandra!