Let’s imagine you’re giving instructions to a friend, but you’re doing it over text message. You write: “Go to the store and buy eggs. ‘Eggs’ means the food, not a person named Eggs.” Sounds silly, right? But you had to clarify because your friend only sees text. They need to know which words are the instructions and which words are the thing you’re talking about.
A computer is the same way, only much more literal. When it reads the code we write, it needs a foolproof system to know, “Okay, THIS part is a command for me to run, and THAT part is just a piece of information—some data—I need to use.” That system is built on Data Types.
In our last lesson, we used alert("Hello") to make a pop-up. The magic that made “Hello” appear as text, and not as some weird code error, was those two little quotation marks: " ". Everything inside them is interpreted as a string.
A string is simply a string of characters, like beads on a necklace. It’s the data type for text. We use it for names, sentences, passwords—anything that’s meant to be read as text and not executed as a command. It’s a way of classifying data to tell the computer, “Hey, treat this as plain old words.”
Now, text isn’t the only kind of data we use. Think about it. If you were telling the computer to do math, you wouldn’t put quotation marks around the numbers, right? You’d just say 2 + 3. That’s because numbers—like 23, -5, or 3.14—are their own data type. The computer recognizes their unique symbols (digits, decimal points) and understands, “Ah, this is a number.” No extra punctuation needed.
Finally, there’s a data type for making decisions. It’s called a Boolean, and it can only ever be one of two values: true or false. That’s it. It’s like a light switch: on or off. We’ll use booleans all the time later to tell our programs, “If this condition is TRUE, do this thing. If it’s FALSE, do something else.”
These three—strings, numbers, and booleans—are fundamental. They are the basic raw materials. Every app or website you’ll ever build is, at its heart, a clever way of combining and manipulating these types of data.
Let’s Get Our Hands Dirty
The best way to understand this isn’t just to read about it—it’s to see it in action. I want you to open up your browser’s JavaScript console right now. It’s easier than it sounds.
- Open your web browser (Chrome, Firefox, Edge, etc.).
- Right-click on any blank part of this page and select “Inspect” or “Inspect Element.”
- Click on the “Console” tab. You’ll see a blank line waiting for you, likely with a little
>prompt.
This console is like a direct chat window with the browser. You can type single lines of code, hit Enter, and see what happens instantly.
Experiment #1: Math with Numbers In the console, type exactly this and hit Enter: 2 + 3 The console will immediately reply with: 5. You just used the number data type to perform a calculation.
Experiment #2: An Alert with a Number Now, let’s use that result in an alert, like we learned before. Type: alert(2 + 3) Hit Enter. A pop-up will appear saying “5”. The computer calculated 2+3 (numbers), got 5 (still a number), and then showed it to you.
Experiment #3: The Secret Decoder Ring – typeof()
Here’s the coolest tool for today. JavaScript gives us a special keyword called typeof(). You put any piece of data inside its parentheses, and it tells you what type it is. It’s like asking the computer, “Hey, how do you classify this?”
Let’s test it.
Checking a Number: Type:
typeof(23)Hit Enter. The console will reply with:"number". Perfect.Checking a String: Now, type:
typeof("My name")Hit Enter. The reply will be:"string". See? The quotation marks told the computer, “This is text,” andtypeof()confirmed it.Checking a Boolean: Finally, type:
typeof(true)Hit Enter. You’ll get back:"boolean".
Isn’t that neat? It’s a direct line into how the computer sees your data. Try mixing it up. What does typeof(2 + 3) give you? (It should say "number", because the result of that math is a number). What happens with typeof("23")? It will say "string" because those quotation marks change everything—it’s now text that happens to look like digits.
Why This All Matters
You might be thinking, “This seems simple.” And you’re right! The concepts are simple, but their importance cannot be overstated. This is the groundwork.
Every single programming language you ever encounter will have these core data types (or very similar ones). The entire logic of your future programs—a login form, a shopping cart calculator, a dynamic weather dashboard—will hinge on you knowing what kind of data you’re working with.
You can’t add the string "5" to the number 10 and expect 15 without telling the computer to convert one type to the other first. Knowing the type is the first step to using the data correctly.
Think of it like tools in a workshop. You have a hammer (strings—for text), a tape measure (numbers—for math and counts), and a switch (booleans—for yes/no decisions). You need to know which tool is in your hand before you start using it, or you’ll end up trying to measure a board with a hammer.
Your Practical Takeaway
Before you close this tab, play in that console for just two more minutes. Don’t just read—type. Ask typeof() questions.
typeof(100)typeof("Hello World")typeof(false)typeof(3.14159)
Get a feel for it. This simple act of checking types will save you hours of debugging later when your programs get more complex. You’ve just learned how to identify the basic building blocks of code.
Next up, we’re going to learn how to store these building blocks for later use. We’re going to talk about variables—the labeled boxes where we keep our strings, numbers, and booleans. It’s where things really start to come together.
For all of that and more, I’ll see you in the next lesson.
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