Key Concepts

Review core concepts you need to learn to master this subject

Restrictions in Naming Properties

Dot Notation for Accessing Object Properties

Objects

Accessing non-existent JavaScript properties

JavaScript Objects are Mutable

JavaScript for...in loop

Properties and values of a JavaScript object

Delete operator

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Restrictions in Naming Properties

// Example of invalid key names
const trainSchedule = {
  platform num: 10, // Invalid because of the space between words.
  40 - 10 + 2: 30, // Expressions cannot be keys.
  +compartment: 'C' // The use of a + sign is invalid unless it is enclosed in quotations.
}

JavaScript object key names must adhere to some restrictions to be valid. Key names must either be strings or valid identifier or variable names (i.e. special characters such as - are not allowed in key names that are not strings).

Objects
Lesson 1 of 1
  1. 1
    Introduction to Objects
    It’s time to learn more about the basic structure that permeates nearly every aspect of JavaScript programming: objects. You’re probably already more comfortable with objects than you think, becau…
    Start
  2. 2
    Creating Object Literals
    Objects can be assigned to variables just like any JavaScript type. We use curly braces, {}, to designate an object literal: let spaceship = {}; // spaceship is an empty object We fill an object…
    Start
  3. 3
    Accessing Properties
    There are two ways we can access an object’s property. Let’s explore the first way— dot notation, .. You’ve used dot notation to access the properties and methods of built-in objects and dat…
    Start
  4. 4
    Bracket Notation
    The second way to access a key’s value is by using bracket notation, [ ]. You’ve used bracket notation when indexing an array: [‘A’, ‘B’, ‘C’][0]; // Returns ‘A’ To use bracket notation to access…
    Start
  5. 5
    Property Assignment
    Once we’ve defined an object, we’re not stuck with all the properties we wrote. Objects are mutable meaning we can update them after we create them! We can use either dot notation, ., or bracke…
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  6. 6
    Methods
    When the data stored on an object is a function we call that a method. A property is what an object has, while a method is what an object does. Do object methods seem familiar? That’s because y…
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  7. 7
    Nested Objects
    In application code, objects are often nested— an object might have another object as a property which in turn could have a property that’s an array of even more objects! In our spaceship o…
    Start
  8. 8
    Pass By Reference
    Objects are passed by reference. This means when we pass a variable assigned to an object into a function as an argument, the computer interprets the parameter name as pointing to the space in me…
    Start
  9. 9
    Looping Through Objects
    Loops are programming tools that repeat a block of code until a condition is met. We learned how to iterate through arrays using their numerical indexing, but the key-value pairs in objects aren’t …
    Start
  10. 10
    Review
    Way to go! You’re well on your way to understanding the mechanics of objects in JavaScript. By building your own objects, you will have a better understanding of how JavaScript built-in objects wor…
    Start

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