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Learn Codepen - 9 Code Examples & CST Typing Practice Test

CodePen is a social development environment and online code editor that allows users to write HTML, CSS, and JavaScript directly in the browser, see live previews, and share projects publicly. It's widely used for front-end experimentation, prototyping, and showcasing web design work.

View all 9 Codepen code examples →

Hello World in CodePen CodePen Button Click Alert CodePen Input Display CodePen Change Background Color CodePen Simple Counter CodePen Toggle Text Visibility CodePen Live Clock CodePen Background Color Cycle CodePen Moving Box Animation

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Updated Nov 26, 2025

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Code Sample Descriptions

1

Hello World in CodePen

<!DOCTYPE html>
<html>
<head>
    <style>
        body { font-family: Arial, sans-serif; text-align: center; margin-top: 50px }
        h1 { color: #FF5722 }
    </style>
</head>
<body>
    <h1>Hello World</h1>
</body>
</html>

A basic CodePen example that displays 'Hello World' with simple styling.

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2

CodePen Button Click Alert

<!DOCTYPE html>
<html>
<head>
    <title>Button Alert</title>
</head>
<body>
    <button id="btn">Click Me</button>
    <script>
        document.getElementById("btn").onclick = () => alert("Hello World")
    </script>
</body>
</html>

A CodePen example showing an alert when a button is clicked.

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3

CodePen Input Display

<!DOCTYPE html>
<html>
<head>
    <title>Input Display</title>
</head>
<body>
    <input id="input" placeholder="Type something">
    <p id="display"></p>
    <script>
        document.getElementById("input").oninput = e => {
        document.getElementById("display").textContent = e.target.value
        }
    </script>
</body>
</html>

Displays the user input live below the input field.

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4

CodePen Change Background Color

<!DOCTYPE html>
<html>
<head>
    <title>Color Change</title>
</head>
<body>
    <button id="colorBtn">Change Color</button>
    <script>
        document.getElementById("colorBtn").onclick = () => {
        document.body.style.backgroundColor = "#4CAF50"
        }
    </script>
</body>
</html>

Changes the page background color when button is clicked.

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5

CodePen Simple Counter

<!DOCTYPE html>
<html>
<head>
    <title>Counter</title>
</head>
<body>
    <p>Count: <span id="count">0</span></p>
    <button id="inc">Increment</button>
    <script>
        let count = 0
        document.getElementById("inc").onclick = () => {
        count++
        document.getElementById("count").textContent = count
        }
    </script>
</body>
</html>

A simple counter incremented by a button click.

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6

CodePen Toggle Text Visibility

<!DOCTYPE html>
<html>
<head>
    <title>Toggle Text</title>
</head>
<body>
    <p id="text">Hello World</p>
    <button id="toggleBtn">Toggle</button>
    <script>
        document.getElementById("toggleBtn").onclick = () => {
        const t = document.getElementById("text")
        t.style.display = t.style.display === "none" ? "block" : "none"
        }
    </script>
</body>
</html>

Toggles visibility of a paragraph when a button is clicked.

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7

CodePen Live Clock

<!DOCTYPE html>
<html>
<head>
    <title>Clock</title>
</head>
<body>
    <p id="clock"></p>
    <script>
        setInterval(() => {
        document.getElementById("clock").textContent = new Date().toLocaleTimeString()
        }, 1000)
    </script>
</body>
</html>

Displays a live updating digital clock.

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8

CodePen Background Color Cycle

<!DOCTYPE html>
<html>
<head>
    <title>Color Cycle</title>
</head>
<body>
    <script>
        const colors = ["red", "green", "blue"]
        let i = 0
        setInterval(() => {
        document.body.style.backgroundColor = colors[i]
        i = (i+1)%colors.length
        }, 1000)
    </script>
</body>
</html>

Cycles through multiple background colors every second.

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9

CodePen Moving Box Animation

<!DOCTYPE html>
<html>
<head>
    <title>Moving Box</title>
    <style>
        #box { width:50px; height:50px; background:red; position:absolute; top:50px; left:0 }
    </style>
</head>
<body>
    <div id="box"></div>
    <script>
        let pos = 0
        setInterval(() => {
        pos += 5
        document.getElementById("box").style.left = pos + "px"
        if(pos > window.innerWidth) pos = 0
        }, 100)
    </script>
</body>
</html>

Moves a red box horizontally across the page continuously.

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Frequently Asked Questions about Codepen

What is Codepen?

CodePen is a social development environment and online code editor that allows users to write HTML, CSS, and JavaScript directly in the browser, see live previews, and share projects publicly. It's widely used for front-end experimentation, prototyping, and showcasing web design work.

What are the primary use cases for Codepen?

Front-end web development and prototyping. Sharing and embedding live demos. Learning and teaching HTML, CSS, and JavaScript. Experimenting with libraries, frameworks, and animations. Showcasing UI/UX design portfolios

What are the strengths of Codepen?

Fast prototyping for front-end ideas. No local setup required. Encourages sharing and community collaboration. Supports a wide range of libraries and frameworks. Visual feedback helps learning and experimentation

What are the limitations of Codepen?

Primarily front-end focused; no backend support by default. Limited file organization in free tier (multi-file Projects are Pro feature). Heavy projects may require external hosting. Offline use is not possible. Some advanced features require Pro subscription

How can I practice Codepen typing speed?

CodeSpeedTest offers 9+ real Codepen code examples for typing practice. You can measure your WPM, track accuracy, and improve your coding speed with guided exercises.

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Learn Codepen - Code Examples & CST Typing Practice Test | CodeSpeedTest