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JavaScript Variables

In programming, a Variable is a container for storing data values. Imagine you are moving into a new house; you put your things into boxes and put a label on each box so you know what's inside.

Variables work exactly like that!

1. How to Create a Variable​

To create (or "declare") a variable in JavaScript, we follow a simple pattern:

let name = "Ajay";
  • let: The keyword that tells the computer we are creating a variable.
  • name: The unique name of the box (the label).
  • =: The assignment operator (it puts the value into the box).
  • "Ajay": The actual data being stored.

2. let vs const​

In modern JavaScript, we have two main ways to create variables. The choice depends on whether the value will change later.

Use let when the value of the variable will change later in your program.

let score = 0;
score = 10; // This is allowed!

3. Rules for Naming Variables​

You can't just name your variables anything. JavaScript has a few strict rules:

  1. No Spaces: Use userAge, not user age.
  2. Camel Case: In JS, we start the first word with a lowercase letter and every word after with a Capital (e.g., isUserLoggedIn).
  3. Start with Letters: Names cannot start with a number.
  4. Meaningful Names: Don't use let x = "Apple". Instead, use let fruit = "Apple". It makes your code easier to read!

4. Using Variables​

Once you store a value, you can use the variable name instead of the value itself.

let city = "Mandsaur";
console.log("I live in " + city); 
// Output: I live in Mandsaur

city = "Indore";
console.log("Now I live in " + city);
// Output: Now I live in Indore

Let's Practice: The Greeting Script​

Try writing this in your script.js:

  1. Create a variable called developerName and store your name in it.
  2. Create a variable called totalProjects and store a number (like 5).
  3. Use console.log to print a message combining both.
const developerName = "A Master"; // Using const because your name doesn't change often
let totalProjects = 3;            // Using let because you will build more!

console.log("Hello, my name is " + developerName);
console.log("I have built " + totalProjects + " projects.");
Always Default to Const

Most professional developers use const for everything by default. They only switch to let if they realize they absolutely need to change the value later. This prevents bugs!

Note on var

You might see some older tutorials using the keyword var. At CodeHarborHub, we avoid var because it is old and can cause strange bugs in your code. Stick to let and const!

Last updated on by Ajay Dhangar