Backend and Frameworks

Table of Content

Compatibility and Performance

Ensuring that JavaScript code runs smoothly across different browsers and optimizing performance are key aspects of web development. This section covers techniques for handling cross-browser compatibility, performance optimization, and best practices for efficient JavaScript execution.

This Privacy Policy describes how Alevio ("we," "our," or "us"), founded and led by Felix Danyluk (CEO and Founder), collects, uses, and discloses your information when you use our application, website, and services (collectively, the "Service").

Important:

Alevio is designed as a privacy-first application. All your personal data is stored locally on your device and is not transferred to our servers unless you explicitly activate cloud functions.

1. Information We Collect

Alevio operates primarily as a local application.
The information stored includes:

Personal information: name and preferences (stored locally only).
Usage data: daily responses and insights (stored locally only).
Device information: app preferences and settings (stored locally only).
AI Chat data: when using AI features, conversation history is stored locally on your device.
Image data: when using vision features, uploaded images are processed locally and may be temporarily stored for AI analysis.
Generated images: DALL-E generated images are saved locally on your device for display purposes.
Usage limits: daily usage tracking for cloud models and image generation is stored locally to enforce fair usage policies.

2. How We Use Your Information

We use the information we collect to:

Provide and maintain our Service
Improve and personalize your experience
Communicate with you about updates and features
Ensure the security and integrity of our Service

3. Data Storage and Security

Your data is stored locally on your device using secure, industry-standard encryption. We do not have access to your personal information unless you explicitly choose to share it through cloud features.

4. Third-Party Services

Alevio may integrate with third-party AI services for enhanced functionality. When using these features, only the necessary data is transmitted to provide the service. We carefully select partners who share our commitment to privacy.

Cloud Services: When you use cloud-based AI models (such as GPT-4o, Claude, or other cloud providers), your messages and uploaded images are sent to these services for processing. We use secure API connections and do not store your data on our servers.
Image Generation: When using DALL-E image generation, your text prompts are sent to OpenAI's servers to generate images. Generated images are returned to your device and stored locally.
Web Search: When using web search features, your search queries are sent to our search partners to retrieve relevant information. Search results are processed and returned to your device.
Apple Shortcuts: When using Apple Shortcuts integration, your device's Shortcuts app may access Alevio through URL schemes. This integration is handled entirely by your device's operating system.

5. Your Rights

You have the right to:

Access your personal data stored on your device
Delete your data at any time through the app settings
Opt out of cloud features and keep all data local
Contact us with any privacy concerns

6. Changes to This Policy

We may update this Privacy Policy from time to time. We will notify you of any changes by posting the new Privacy Policy on this page and updating the "Last Updated" date.

7. Contact Us

If you have any questions about this Privacy Policy or our privacy practices, please contact us at:

privacy.alevio@gmail.com

Handling Cross-Browser Compatibility

Different browsers interpret JavaScript slightly differently. Developers must ensure that their code works consistently across modern browsers like Chrome, Firefox, Safari, Edge, and even older versions of Internet Explorer when necessary.

Feature Detection Using `if` Statements

Before using a feature, check if the browser supports it.

if ("geolocation" in navigator) {
  navigator.geolocation.getCurrentPosition(position => {
    console.log("Latitude:", position.coords.latitude);
  });
} else {
  console.log("Geolocation is not supported in this browser.");
}

Using `try...catch` for Fallbacks

For features that may throw errors in unsupported browsers:

try {
  let speech = new SpeechSynthesisUtterance("Hello");
  window.speechSynthesis.speak(speech);
} catch (error) {
  console.log("Speech API not supported.");
}

Using Polyfills

A polyfill is JavaScript code that provides modern functionality in older browsers.

Example: Adding fetch() support for older browsers:

<script src="https://cdnjs.cloudflare.com/ajax/libs/fetch/3.6.2/fetch.min.js"></script>

Reducing JavaScript Execution Time

Minifying JavaScript removes unnecessary characters to reduce file size.

Use Terser or UglifyJS to minify scripts:

Load scripts asynchronously to prevent blocking the page load.

async: Loads in parallel but executes immediately.

defer: Loads in parallel and executes after HTML parsing is complete.

<script src="script.js" async></script>
<script src="script.js" defer></script>

Reduce Unnecessary DOM Manipulation

Frequent DOM changes can slow down performance.

Inefficient:

for (let i = 0; i < 100; i++) {
  document.body.appendChild(document.createElement("p"));
}

Efficient (using DocumentFragment):

let fragment = document.createDocumentFragment();
for (let i = 0; i < 100; i++) {
  let p = document.createElement("p");
  fragment.appendChild(p);
}
document.body.appendChild(fragment);

Optimizing Loops and Event Listeners

Use Efficient Loops

forEach() and map() are convenient but for loops can be faster for large datasets.

let arr = new Array(100000).fill(0);

console.time("forEach");
arr.forEach(num => num + 1);
console.timeEnd("forEach");

console.time("for-loop");
for (let i = 0; i < arr.length; i++) {
  arr[i] + 1;
}

console.timeEnd("for-loop");

Throttle and Debounce Events

Expensive event listeners (e.g., scroll, resize) can degrade performance.

Debouncing ensures the function runs only after the event has stopped firing.
Throttling ensures the function runs at a fixed interval, even if the event continues firing.

Debounce Example

function debounce(func, delay) {
  let timer;
  return function () {
    clearTimeout(timer);
    timer = setTimeout(() => func.apply(this, arguments), delay);
  };
}
  
window.addEventListener("resize", debounce(() => {
  console.log("Resize event fired!");
}, 300));

Throttle Example

function throttle(func, limit) {
  let lastCall = 0;
  return function () {
    let now = Date.now();
    if (now - lastCall >= limit) {
      lastCall = now;
      func.apply(this, arguments);
    }
  };
}
  
window.addEventListener("scroll", throttle(() => {
  console.log("Scroll event fired!");
}, 200));

Use Web Workers for Heavy Computations

Web Workers allow running JavaScript in the background without blocking the main thread.

Creating a Web Worker

let worker = new Worker("worker.js");

worker.postMessage("Start");
  
worker.onmessage = event => {
  console.log("Worker Response:", event.data);
};

worker.js

self.onmessage = () => {
  let result = 0;
  for (let i = 0; i < 1e9; i++) {
    result += i;
  }
  postMessage(result);
};

Use Efficient Data Structures

Use Maps Instead of Objects for Large Datasets

let obj = {};
let map = new Map();
  
map.set("key1", "value1");
console.log(map.get("key1"));

Use Set for Unique Values

let uniqueNumbers = new Set([1, 2, 3, 3, 4]);
console.log(uniqueNumbers.size); // Outputs: 4

Conclusion

Optimizing JavaScript ensures better browser performance and compatibility. This section covered techniques for reducing execution time, handling memory leaks, improving event handling, and using efficient data structures. The next section will focus on JavaScript in the Backend with Node.js, covering server-side development with JavaScript.