React components are reusable pieces of UI (user interface) code that are written in JavaScript. React components are self-contained pieces of code that manage their own state at runtime and that can be used in other components. They can be used to create complex user interfaces which are easy to manage and maintain. Components are often broken down into smaller pieces called components, making it easier to write and reuse code. React components use a syntax known as JSX, which allows developers to write HTML-like syntax within their JavaScript code. As a result, React components can be very powerful, allowing developers to create user interfaces that are both fast and responsive.

Yes, it is possible to code a calculator. Depending on the level of complexity, the programming language used can vary. For instance, a basic calculator can be made with HTML and JavaScript. Here's an example of a calculator written in JavaScript:

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// Create variables
let input1 = document.querySelector('#input1'); 
let input2 = document.querySelector('#input2'); 
let addButton = document.querySelector('#addButton');
let result = document.querySelector('#result');

// Button click calculation
addButton.addEventListener('click', () => {
    result.value = parseFloat(input1.value) + parseFloat(input2.value);
});

To learn more about making a calculator in JavaScript, you may refer to the MDN Web Docs here.

Common node.js interview questions include:

• What is Node.js used for?
• What is the difference between Node.js and JavaScript?
• What is asynchronous programming?
• What are the pros and cons of using an asynchronous programming paradigm?
• What is an event loop?
• What libraries and frameworks have you used in your projects?
• How do you debug a Node.js application?
• How do you unit test a Node.js application?
• How would you secure a Node.js application?
• Describe the most complex project you’ve built with Node.js.
• How do streams work in Node.js?
• What is the responsibility of the incubator in the Node.js process?
• What is callback hell and how can it be avoided?
• What do you need to keep in mind when scaling a Node.js application?

See this Stack Overflow answer for an in-depth look into Node.js interview questions.

A sticky header is a feature of many websites where the header scrolls with the page, but remains visible at the top at all times. Commonly this is implemented using JavaScript or CSS with a technique known as "position: sticky". Here is an example of CSS code for a sticky header:

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head {
   position: sticky;
   top: 0;
}

For more detailed explanation, see this article.

You can use the fetch API to retrieve data from an API in JavaScript. Once you've got the response, you can log the first comment using the json method to convert the object into a JSON string. Use console.log to log the result:

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fetch('https://api.example.com/comments')
  .then(response => response.json())
  .then(data => {
    console.log(data.comments[0]);
  });

Using JavaScript, you can use the Fetch API to send an HTTP request and get the API response.

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fetch("https://jsonplaceholder.typicode.com/comments")
  .then(res => res.json())
  .then(data =>  {
    console.log(data);
  });

You can also use a library like Axios to make the same request:

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axios.get("https://jsonplaceholder.typicode.com/comments")
  .then(res => {
  console.log(res.data);
});

Learn more:

• Fetch API
• Axios

To extract data from a Node List within the developers console, you can use JavaScript. Using the forEach() method, you can iterate through the position of each node to access its data. For example:

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const nodeListExample = document.querySelectorAll('ul li');
nodeListExample.forEach(node => {
  console.log(node.innerHTML);
});

This will iterate through each element inside the node list and access its individual data (in this case, the HTML content within each list item).

Further Resources:

• MDN Docs - NodeList.forEach()

Fetch requests in JavaScript are an essential part of modern web development. To send a fetch request to an API, you can use the fetch() method, which is part of the Fetch API. Here is an example of a GET request:

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fetch('https://api.example.com/endpoint')
  .then(response => response.json())
  .then(data => console.log(data))
  .catch(error => console.error(error))

In the example above, the fetch() method takes in a URL as a parameter, then returns a Promise object which provides access to the response of the request. The .then() method, which is part of Promises, is a way to handle both a successful response or an error in your fetch request.

You can create a button that will change language on your website using JavaScript. On HTML you will need to create a button element:

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<button id="btn">Change Language</button>

Then add an onclick instruction inside the button element in the HTML:

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<button id="btn" onclick="changeLang()">Change Language</button>

You will also need to add a JavaScript function to set the language of the page. For example, the following code will create a variable to hold the language and then checks if the language variable is set to en or es and changes the language accordingly:

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function changeLang() {
    var language = getCookie("lang");
    if (test == "en") {
        setCookie("lang", "es", 365);
        window.location.reload();
    } else {
        setCookie("lang", "en", 365);
        window.location.reload();
    }    
}

You can get more information and a more detailed explanation in this article: How to Add a Language Switcher to Your Site

Good luck!

Ads can be dynamically inserted on the internet using JavaScript by having a script reference the desired ad and then insert it into the webpage. The script runs when the webpage is loaded, and it references the ad from an ad server.

For example, this bit of code would reference and insert an ad from the Adobe Ad Serve Ad Server.

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<script type="text/javascript">
   var ad="<a href='http://www.adobe.com' target='_blank'><img src='http://www.adobe.go/ads/ad.jpg' width='728' height='90' border='0' alt=''></a>"
   document.write(ad);
</script>

When the script runs, it references the ad from the specified ad server, ads.adobe.com. The script then inserts the ad into the webpage where the code appears.

More information on dynamically inserting ads using JavaScript can be found here.

Below is an example of Javascript code that creates a basic music player. Code blocks are included so you can see the various components needed to create the player.

HTML

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<div class="player">
  <audio src="https://example.com/tunes/song.mp3" id="music" preload="auto"></audio>
  <div class="info">
    <div class="left">
      <span class="artist">Artist Name</span>
      <span class="title">Song Title</span>
    </div>
    <div class="right">
      <span class="time">00:00</span>
    </div>
  </div>
  <div class="controls">
    <div class="play">&#9654;</div>
    <div class="pause">||</div>
  </div>
</div>

CSS

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.player {
  width: 250px;
  padding: 10px;
  background: #444;
  margin: 10px auto;
  box-shadow: 0 0 10px rgba(0, 0, 0, 0.5);
}

.info {
  position: relative;
  font-size: 14px;
  padding: 10px;
  color: #ccc;
  line-height: 1;
  text-align: center;
}

.left span {
  display: block;
}

.time {
  position: absolute;
  right: 10px;
  top: 10px;
}

.controls {
  padding: 10px 0;
  text-align: center;
}

.controls div {
  display: inline-block;
  margin: 0 10px;
  font-size: 24px;
}

JAVASCRIPT

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// Cache DOM
var audio = document.getElementById("music");
var time = document.querySelector(".time");

// Bind events
document.querySelector(".play").addEventListener("click", play);
document.querySelector(".pause").addEventListener("click", pause

Interactive background is a feature that enables users to generate a background that reacts to mouse movement. To achieve this effect, a combination of HTML, CSS, and JavaScript can be used.

In HTML, add a <div> element inside which elements for the background need to be added.

In CSS, set the size of the <div> to 100% in order to have the background fill the entire page. To create the animation, a keyframe animation should be defined. The animation should change the parameters of the background elements so they move. An example animation could be:

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@keyframes example {
  0%   { transform: rotate(0deg); left: 0; }
  100% { transform: rotate(360deg); left: 50%; }
}

In JavaScript, a function should be created that triggers the animation. A common way to trigger the animation is to add an onmousemove event listener that calls the animation function. An example JavaScript code looks like this:

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window.addEventListener("mousemove", () => {
  document.querySelector("div").style.animation = "example 2s linear infinite";
});

For more details about how to do interactive backgrounds, please refer to this article.

Replacing something in an array can be accomplished in many different programming languages. For example, in JavaScript, the splice() method can be used to remove existing elements from an array and then replace them with new elements.

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const fruits = ["Banana", "Orange", "Apple", "Mango"];

// Removing 1 element at index 0
fruits.splice(0, 1);

// insert 1 element at index 0
fruits.splice(0, 0, "Lemon");

// change the element at index 0
fruits.splice(0, 1, "Kiwi");

console.log(fruits); 
// Output: ["Kiwi", "Orange", "Apple", "Mango"]

For more information on how to use the splice() method see this MDN article.

The less-than sign < is most commonly used to indicate the beginning of a tag when writing HTML and XML code. When writing other types of code, the less-than sign may be used to compare two data objects, such as variables. For example, in JavaScript we can conditionally execute a block of code using an if statement like this:

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if (x < y) {
    // execute this block of code
}

addEventListener() is a JavaScript method that allows for an action (event) to be listened for and responded to. This can be any type of event, such as clicking a button, hovering over a certain element, etc. When the specified event occurs, the code inside the event listener is run. For example, in HTML:

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<button onclick="console.log('You clicked me!')">Click me!</button>

The above code will log 'You clicked me!' to the console when the button is clicked.

The same can be achieved using addEventListener():

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let button = document.querySelector('button');

button.addEventListener('click', function() {
  console.log('You clicked me!')
})

This code sets the variable button to the HTML element with the <button> tag, and then a click event listener is added to the button object that logs 'You clicked me!' to the console when the button is clicked.

You can use JavaScript to create a simple hamburger menu. Here's an example:

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// Get all the elements for the hamburger
let navLinks = document.querySelector('.navLinks');
let hamburgerMenu = document.querySelector('.hamburgerMenu');

// On click toggle the class on the hamburger 
hamburgerMenu.addEventListener('click', () => {
  navLinks.classList.toggle('open');
});

You can also use CSS and HTML in combination. Here's an example from W3Schools.

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/* The "responsive" class is added to the topnav with JavaScript when the user clicks on the icon. This class makes the topnav look good on small screens (display the links vertically instead of horizontally) */
@media screen and (max-width: 600px) {
  .topnav.responsive {position: relative;}
  .topnav.responsive a.icon {
    position: absolute;
    right: 0;
    top: 0;
  }
  .topnav.responsive a {
    float: none;
    display: block;
    text-align: left;
  }
}

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<div class="topnav" id="myTopnav">
  ...
  <a href="javascript:void(0);" class="icon" onclick="myFunction()">
    <i class="fa fa-bars"></i>
  </a>
</div>

Hope this helps! :smile:

Yes, a function can be placed in another function in JavaScript. When you declare a function inside another function, it's called a nested function. The inner function will have access to all the variables of the outer function, even after the outer function has returned.

Below is an example of a nested function:

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function outerFunction() {
  let outerVariable = "outer";

  function innerFunction() {
    console.log(outerVariable);
  }

  return innerFunction;
}

In JavaScript, an object is a collection of properties, and a property is an association between a name (or key) and a value. A property's value can be a function, in which case the property is known as a method. Objects are the building blocks for modern JavaScript applications and are used to store and manage data.
For more information and example, please see MDN's introduction to Objects.

In order to create a React component, you can use either JavaScript or TypeScript depending on your preference. Here's an example in JavaScript:

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class MyComponent extends React.Component {
  render() {
    return (
      <h1>Hello World!</h1>
    );
  }
}

In TypeScript, you can create a component like this:

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Typescript

class MyComponent extends React.Component<Props, State> {
  render() {
    return <h1>Hello World!</h1>;
  }
}

To learn more about React components in JavaScript and TypeScript, please refer to this React documentation page: https://reactjs.org/docs/components-and-props.html.

This can be solved using a combination of looping and conditional statements. Below is an example solution in JavaScript.

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function isSpecialNumber(input) {
  let numString = input.toString();  // Convert input to a string

  // Loop through each character in number string
  for (let i = 0; i < numString.length; i++) {
    // Convert current char to int
    let currentNum = parseInt(numString.charAt(i));
    // Check if current number is not in the specified range
     if (currentNum > 5) {
      return false; // Not a special number
    }
  }

  return true; // All chars in the range -> Special Number
}

References:

• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/charAt

React.js and Angular are two popular open-source JavaScript frameworks used for front-end development.

React.js is a JavaScript library created by Facebook for building user interfaces. It uses a component-based structure, which allows developers to break down complex user interfaces into smaller, more manageable pieces. React.js offers more flexibility than traditional Model-View-Controller (MVC) frameworks, allowing developers to create custom components for their projects.

Angular is a full-featured MVC framework from Google. It allows developers to create single page web applications by combining data from a Model layer with components from a View layer. Angular's component-based architechture insulates developers from many of the complexities of modern web programming, allowing them to easily create, update and delete objects.

Both React.js and Angular offer different approaches to web development, and thus are suitable for different use cases. For some projects, React.js might be a better choice due to its flexibility, while Angular could be a better choice in other cases due to its robust architecture. Ultimately, the decision on which framework to use should come down to the project at hand and developers' preferences.

For more information, see the following link: https://developer.telerik.com/topics/web-development/angular-vs-react-which-framework-should-you-choose-your-next-project/

Axios is an open-source library for making HTTP requests from Node.js or the browser. It supports the Promise API and provides utilities for vanillajs, React, and Vue.js in order to make HTTP requests.

Axios works using the standard Promise API, making code more readable and asynchronous without having to use callbacks. This works by making an XMLHttpRequest in supported browsers, or a XDomainRequest (works in IE 9 and IE 8) in legacy browsers.

Code example with Axios (in Javascript):

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axios.get('/user?ID=12345')
  .then(function (response) {
    // handle success
    console.log(response);
  })
  .catch(function (error) {
    // handle error
    console.log(error);
  })
  .finally(function () {
    // always executed
  });

For more information see: Axios Documentation.

To add AM/PM in time with JavaScript you can use toLocaleTimeString() method. This method converts the time value to a time string using a locale and time options.

For example:

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let currentDate = new Date();
let am_pm = currentDate.toLocaleTimeString();
console.log(am_pm); // 12:48:20 PM

More information can be found on MDN Docs and on W3Schools.

You can make an automatic image slider using JavaScript. The basic idea is to have a series of slides with images and corresponding captions, and have those slides transition automatically by setting the transition property of the slides to a specific time interval. A basic example is given below:

HTML

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<div class="slideshow">
  <div class="slide">
    <img src="image1.jpg" alt="Image 1">
    <p> Caption 1 </p>
  </div>
  <div class="slide">
    <img src="image2.jpg" alt="Image 2">
    <p> Caption 2 </p>
  </div>
  <div class="slide">
    <img src="image3.jpg" alt="Image 3">
    <p> Caption 3 </p>
  </div>
</div>

CSS

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.slideshow {
  max-width: 600px;
  margin: auto;
  position: relative;
}
.slide {
  display: none;
}

JavaScript

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// set index and transition delay
let index = 0;
let transitionDelay = 2000;

// get div containing the slides
let slideContainer = document.querySelector(".slideshow");
// get the slides
let slides = slideContainer.querySelectorAll(".slide");

// set transition delay for slides
for (let slide of slides) {
  slide.style.transition = `all ${transitionDelay/1000}s linear`;
}

// show the first slide
showSlide(index);

// show a specific slide
function showSlide(slideNumber) {
  slides.forEach((slide, i) => {
    slide.style.display = i == slideNumber ? "block" : "none";
  });
  // next index
  index++;
  // go back to 0 if at the end of slides
  if (index >= slides.length) {
    index = 0;
  }
}

// transition to next slide every x seconds
setInterval (() => showSlide(index), transitionDelay);

To convert a timestamp to hours in JavaScript, you can use the getHours() method from the Date object and pass the timestamp as an argument. The following example shows how it would look:

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const timestamp = 1558686613;
const date = new Date(timestamp * 1000);
const hours = date.getHours();
console.log(hours); // Output: 9