Computer Science
Grade 8
20 min
Web Application Project
Web Application Project
Tutorial Preview
1
Introduction & Learning Objectives
Learning Objectives
Explain the role of JavaScript in a web application.
Select HTML elements using `document.getElementById()`.
Create and call a JavaScript function to perform a specific task.
Use an `addEventListener` to make a webpage interactive.
Manipulate the content of an HTML element using `.innerHTML`.
Declare variables to store and update data like a score or a name.
Use an `if/else` statement to make a simple decision in their code.
Ever clicked a 'like' button and watched the number go up instantly? That's JavaScript in action! 🚀 Let's learn how to make our own web pages come alive.
In this chapter, you will learn the basics of JavaScript, the programming language that adds interactivity to websites. We will connect JavaScript to our HTML...
2
Key Concepts & Vocabulary
TermDefinitionExample
VariableA named container for storing data. You can think of it like a labeled box where you can keep a number, text, or other information that might change.`let score = 0;` creates a variable named 'score' and stores the number 0 in it.
FunctionA reusable block of code that performs a specific task. You give it a name and can 'call' it whenever you need that task done.`function showMessage() { alert('Hello!'); }` defines a function that will pop up a 'Hello!' message when called.
DOM (Document Object Model)A tree-like representation of an HTML document. JavaScript uses the DOM to find, change, add, or delete HTML elements and their content.JavaScript can use the DOM to find an HTML element with `id='title'` and then...
3
Core Syntax & Patterns
Selecting an Element by ID
document.getElementById('elementID')
Use this pattern to grab a specific HTML element from the page so you can interact with it in JavaScript. The 'elementID' must exactly match the `id` attribute in your HTML tag.
Creating a Function
function functionName() {
// code to run goes here
}
This is the standard way to define a named function. The code inside the curly braces `{}` will only run when the function is called by its name, like `functionName();`.
Setting up an Event Listener
element.addEventListener('eventName', functionToRun);
This is the most common way to make a page interactive. You first select an `element`, then specify the `eventName` to listen for (like 'click'), and finally provide...
4 more steps in this tutorial
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Challenging
You are building a game where a `score` variable tracks points. A message element with `id="result"` should display 'You Win!' if the score is 50 or more, otherwise it should display 'Game Over'. Which code snippet correctly implements this logic?
A.if (score > 50) { result.innerHTML = 'You Win!'; } else { result.innerHTML = 'Game Over'; }
B.if (score >= 50) { result.innerHTML = 'You Win!'; } else { result.innerHTML = 'Game Over'; }
C.if (score = 50) { result.innerHTML = 'You Win!'; } else { result.innerHTML = 'Game Over'; }
D.if (score >= 50) { result.innerHTML = 'Game Over'; } else { result.innerHTML = 'You Win!'; }
Challenging
The 'Simple Click Counter' example has an `updateCounter` function that increases a count. How would you write a new function, `decreaseCounter`, to make a button that *decreases* the count by 1?
A.function decreaseCounter() { count = count * -1; display.innerHTML = count; }
B.function decreaseCounter() { count = 1 - count; display.innerHTML = count; }
C.function decreaseCounter() { count = count - 1; display.innerHTML = count; }
D.function decreaseCounter() { count = count / 1; display.innerHTML = count; }
Challenging
A student's click counter only works for the first click (it goes from 0 to 1) and then gets 'stuck' at 1 on all future clicks. What is the most likely logical error in their `updateCounter` function?
A.The line `button.addEventListener(...)` is mistakenly placed inside the function.
B.The line `let count = 0;` is mistakenly placed inside the function.
C.The line `display.innerHTML = count;` is the first line in the function instead of the last.
D.The line `const display = document.getElementById(...)` is mistakenly placed inside the function.
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