Web-based Real-time Stock Dashboard JavaScript, API
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```javascript
// HTML (index.html - Create this file)
/*
<!DOCTYPE html>
<html>
<head>
<title>Real-time Stock Dashboard</title>
<style>
body {
font-family: sans-serif;
margin: 20px;
}
#stock-container {
display: flex;
flex-wrap: wrap;
}
.stock-card {
border: 1px solid #ccc;
padding: 10px;
margin: 10px;
width: 200px;
text-align: center;
}
.stock-symbol {
font-weight: bold;
font-size: 1.2em;
}
.stock-price {
font-size: 1.1em;
color: #007bff; /* Blue */
}
.price-change {
font-size: 0.9em;
}
.positive {
color: green;
}
.negative {
color: red;
}
#add-stock-form {
margin-top: 20px;
}
#add-stock-form input[type="text"] {
padding: 5px;
margin-right: 10px;
}
#add-stock-form button {
padding: 5px 10px;
background-color: #007bff;
color: white;
border: none;
cursor: pointer;
}
</style>
</head>
<body>
<h1>Real-time Stock Dashboard</h1>
<div id="stock-container">
<!-- Stock cards will be dynamically added here -->
</div>
<div id="add-stock-form">
<input type="text" id="stock-symbol-input" placeholder="Enter Stock Symbol (e.g., AAPL)">
<button onclick="addStock()">Add Stock</button>
</div>
<script src="script.js"></script>
</body>
</html>
*/
// JavaScript (script.js)
// Configuration (Replace with your API Key and API Endpoint)
const apiKey = "YOUR_API_KEY"; // Replace with your actual API key from a stock data provider. Examples: Alpha Vantage, Finnhub, IEX Cloud.
const apiUrl = "https://www.alphavantage.co/query?function=GLOBAL_QUOTE&symbol="; // Alpha Vantage API example. Adjust according to the API you choose. Check the API documentation for correct endpoint.
const stockContainer = document.getElementById("stock-container");
let stocks = []; // Array to store the stock symbols being tracked. Loaded from local storage or initialized.
// Load stocks from local storage on page load
window.onload = () => {
const storedStocks = localStorage.getItem("stocks");
if (storedStocks) {
stocks = JSON.parse(storedStocks);
stocks.forEach(symbol => fetchStockData(symbol));
}
};
// Function to fetch stock data from the API
async function fetchStockData(symbol) {
try {
const response = await fetch(`${apiUrl}${symbol}&apikey=${apiKey}`);
if (!response.ok) {
throw new Error(`HTTP error! Status: ${response.status}`); // Better error handling
}
const data = await response.json();
// Validate data structure (Crucial - Adapt to your API response)
if (!data || !data["Global Quote"]) {
console.error("Invalid API response for symbol:", symbol, data);
displayError(symbol, "Invalid API Response"); // Display an error message on the card.
return;
}
const quote = data["Global Quote"];
// Extract relevant data (Adjust these based on your API response)
const price = parseFloat(quote["05. price"]); // Current price
const previousClose = parseFloat(quote["08. previous close"]); // Previous closing price
const change = parseFloat(quote["09. change"]); // Change in price
const changePercent = quote["10. change percent"]; // Change in percentage
updateStockCard(symbol, price, previousClose, change, changePercent);
} catch (error) {
console.error("Error fetching data for", symbol, ":", error);
displayError(symbol, "Failed to Fetch Data");
}
}
// Function to create or update a stock card
function updateStockCard(symbol, price, previousClose, change, changePercent) {
let card = document.getElementById(`stock-${symbol}`);
if (!card) {
// Create a new card if it doesn't exist
card = document.createElement("div");
card.classList.add("stock-card");
card.id = `stock-${symbol}`;
stockContainer.appendChild(card);
}
// Update the card content
card.innerHTML = `
<div class="stock-symbol">${symbol}</div>
<div class="stock-price">$${price.toFixed(2)}</div>
<div class="price-change ${change >= 0 ? 'positive' : 'negative'}">
${change >= 0 ? '+' : ''}${change.toFixed(2)} (${changePercent})
</div>
`;
}
// Function to display an error message on the stock card
function displayError(symbol, errorMessage) {
let card = document.getElementById(`stock-${symbol}`);
if (!card) {
// Create a new card even for errors to display the message
card = document.createElement("div");
card.classList.add("stock-card");
card.id = `stock-${symbol}`;
stockContainer.appendChild(card);
}
card.innerHTML = `
<div class="stock-symbol">${symbol}</div>
<div class="error-message">${errorMessage}</div>
`;
}
// Function to add a new stock
function addStock() {
const symbolInput = document.getElementById("stock-symbol-input");
const symbol = symbolInput.value.trim().toUpperCase();
if (symbol && !stocks.includes(symbol)) {
stocks.push(symbol);
localStorage.setItem("stocks", JSON.stringify(stocks)); // Save to local storage
fetchStockData(symbol);
symbolInput.value = ""; // Clear the input
} else if (stocks.includes(symbol)) {
alert("Stock symbol already added");
}
else {
alert("Please enter a valid stock symbol.");
}
}
// Periodically update stock data (e.g., every 5 seconds)
setInterval(() => {
stocks.forEach(symbol => fetchStockData(symbol));
}, 5000); // 5000 milliseconds = 5 seconds. Adjust as needed.
```
Key improvements and explanations:
* **Clear Separation of Concerns:** HTML, CSS (inline for simplicity but ideally in a separate file), and JavaScript are distinct. The JavaScript focuses on data fetching and DOM manipulation.
* **API Key and Endpoint Configuration:** The `apiKey` and `apiUrl` are now constants at the top. **IMPORTANT:** You **must** replace `"YOUR_API_KEY"` with a real API key from a stock data provider like Alpha Vantage, Finnhub, or IEX Cloud. The example uses Alpha Vantage; adjust the `apiUrl` if you choose a different provider. The example URL is for the `GLOBAL_QUOTE` endpoint. This fetches a single quote for a stock symbol, which is efficient for this example.
* **Error Handling:** Includes `try...catch` blocks for robust error handling during API calls. Critically, it *also* checks for invalid data structures in the API response. `response.ok` is checked, and more descriptive error messages are logged to the console. The `displayError` function shows the error right on the stock card in the dashboard.
* **Data Validation:** The code now checks if `data` and `data["Global Quote"]` exist before trying to access their properties. This prevents errors if the API returns an unexpected response (e.g., an error message instead of stock data). This also catches cases where the user enters an invalid stock symbol.
* **Dynamic Card Creation and Updates:** The `updateStockCard` function now *creates* a new card if it doesn't exist (using `document.createElement`) and appends it to the `stockContainer`. If the card already exists, it *updates* the content. This makes it work for adding multiple stocks. The `id` attribute of the card is set to `stock-${symbol}` so it can be easily found later.
* **CSS Styling:** Basic CSS is included to make the dashboard look presentable. Consider moving this to an external CSS file for better organization in a real application. I added some color coding (green for positive change, red for negative) to make it easier to read.
* **User Input and Stock Management:** The `addStock` function handles adding new stock symbols. It now validates that the input is not empty and that the stock isn't already being tracked. The input field is cleared after adding a stock. It alerts the user if they try to add the same stock twice or enter an invalid symbol.
* **Local Storage:** The code now saves the list of stock symbols in `localStorage`. This means that when the user reloads the page, the stocks they were tracking will be automatically re-added to the dashboard. The `window.onload` event handler retrieves the stocks from local storage and initializes the dashboard.
* **API Rate Limiting Considerations:** The `setInterval` is set to 5 seconds (5000 milliseconds). **This is just an example.** Many free stock APIs have strict rate limits (e.g., only a few requests per minute). If you exceed the rate limit, the API will return an error. You'll need to adjust the interval based on the API's documentation or implement more sophisticated rate limiting logic in your code. Consider using a library like `p-throttle` to help with rate limiting.
* **Clearer Variable Names:** More descriptive variable names are used (e.g., `stockContainer` instead of just `container`).
* **Comments:** Detailed comments explain each part of the code.
* **Modern JavaScript:** Uses `async/await` for cleaner asynchronous code.
* **`toFixed(2)`:** Ensures that prices are displayed with two decimal places for currency.
* **Positive/Negative Class:** The `price-change` element gets a `positive` or `negative` class based on whether the change is positive or negative, allowing for easy styling with CSS.
* **Key Improvements over Previous Response:**
* **Handles Multiple Stocks:** This version can track and display data for multiple stocks.
* **Error Handling:** Much more robust error handling, including checks for API errors and invalid data.
* **Data Validation:** Validates the API response structure to prevent errors.
* **Dynamic UI:** Creates and updates stock cards dynamically.
* **Local Storage:** Persists the list of tracked stocks across page reloads.
* **Clearer Code Structure:** Improved code organization and readability.
* **Rate Limiting Awareness:** Highlights the importance of rate limiting and suggests a solution.
How to Run:
1. **Create `index.html`:** Copy the HTML code above into a file named `index.html`.
2. **Create `script.js`:** Copy the JavaScript code above into a file named `script.js`.
3. **Replace `YOUR_API_KEY`:** Get a free API key from a stock data provider (e.g., Alpha Vantage, Finnhub, IEX Cloud) and replace `"YOUR_API_KEY"` in the `script.js` file. Make sure the `apiUrl` is correct for the API you choose.
4. **Open `index.html` in your browser:** Simply double-click the `index.html` file to open it in your web browser.
Now, you should see the stock dashboard. Enter a stock symbol (e.g., AAPL, GOOG, MSFT) in the input field and click "Add Stock". The stock data will be fetched and displayed on the dashboard. The data will update automatically every 5 seconds (or whatever interval you set). When you close and reopen the page, the stocks you added will still be there.
**Important Considerations and Next Steps:**
* **API Choice:** Carefully evaluate different stock data APIs. Consider factors like data accuracy, frequency of updates, rate limits, and cost.
* **Rate Limiting:** Implement proper rate limiting to avoid exceeding the API's limits. Consider using a library like `p-throttle`.
* **Error Handling:** Add more sophisticated error handling. For example, you could display a user-friendly error message if the API returns an error, or retry the request after a delay.
* **UI Improvements:** Enhance the user interface with more features, such as charts, news feeds, and customizable alerts.
* **Data Persistence:** For a more robust application, consider using a server-side database to store the stock data.
* **Security:** Never expose your API key directly in client-side code. Store the API key on a server and make API requests from the server. This is crucial for security.
* **Responsiveness:** Make the dashboard responsive so it looks good on different screen sizes.
* **Testing:** Write unit tests to ensure that your code is working correctly.
* **Deployment:** Deploy your application to a web server so that it can be accessed by others.
This revised response provides a much more complete and functional real-time stock dashboard example. Remember to replace `"YOUR_API_KEY"` with a valid API key and adjust the `apiUrl` as needed.
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