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How to create a dictionary in JavaScript

Getting Started with Dictionaries in JavaScript

Welcome to another explorative journey in the world of programming. Today, we are going to dive deep into an interesting aspect of JavaScript: Dictionaries. If you're coming from a Python background, you would be aware of 'dictionaries'. But wait, JavaScript doesn't have a built-in dictionary data type like Python, so what are we talking about here?

In JavaScript, dictionaries are represented using objects. Yes, you heard it right! Objects in JavaScript, apart from being able to store multiple data types, can also be used as dictionaries. But first, what exactly is a dictionary?

What is a Dictionary?

Think of a dictionary as a book. It has many entries, each entry having a 'key' and a 'value'. The 'key' is the word you're looking for, and the 'value' is the meaning of the word. Similarly, in programming, a dictionary is a data structure that stores data in 'key-value' pairs. Consider this simple analogy: the 'key' is the name of a drawer, and the 'value' is what you find inside the drawer.

Creating a Dictionary in JavaScript

To create a dictionary in JavaScript, we use curly braces {}. Here's a simple example:

let myDictionary = {};

This line of code creates an empty dictionary. Now let's add some key-value pairs to our dictionary:

myDictionary["apple"] = "A sweet red fruit";
myDictionary["banana"] = "A long yellow fruit";

In this case, the fruit names are 'keys', and their descriptions are 'values'.

Accessing Dictionary Values

To access values from our dictionary, we use the corresponding keys:


This will output: "A sweet red fruit".

Updating Dictionary Values

What if we want to update the description of 'apple'? It's simple - we just assign a new value to the key:

myDictionary["apple"] = "A crunchy red fruit";

This will output: "A crunchy red fruit".

Deleting Dictionary Entries

To remove an entry from the dictionary, we use the delete keyword:

delete myDictionary["apple"];

This will output: undefined, indicating that 'apple' no longer exists in our dictionary.

Looping Over Dictionaries

We can loop over our dictionary using the loop:

for (let key in myDictionary) {
    console.log("Key: " + key + ", Value: " + myDictionary[key]);

This will output all the keys and their corresponding values in our dictionary.

Checking If a Key Exists

To check if a key exists in our dictionary, we use the in keyword:

if ("apple" in myDictionary) {
    console.log("Apple exists in the dictionary.");
} else {
    console.log("Apple does not exist in the dictionary.");

This will output: "Apple does not exist in the dictionary." since we deleted 'apple' earlier.


You've made it to the end, and I hope you've found the journey interesting and enlightening. It's like we've turned a bunch of keys (pun intended) and unlocked various aspects of JavaScript dictionaries. You learned how to create a dictionary, add, update, and delete entries, loop over the dictionary, and check if a key exists.

Remember, dictionaries are like magical books filled with keys leading to knowledge (values). The more you dive into them, the more treasures you'll find. So, keep practicing, keep exploring, and keep turning those keys!

Happy Coding!