In JavaScript, alert() is a built-in function that displays an alert box with a specified message and an OK button.

Syntax:

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alert(message);

Example:

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alert("This is an alert box!");

console.log() is a function in JavaScript used to print content to the console. When the script is run, the output of the console.log() statement can be seen in the console.

For example, the following code prints the statement 'Hello World!' to the console:

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console.log('Hello World!');

This is a JavaScript conditional statement that checks if the variable firstName is not empty. If it is not empty, it will execute the code inside the block, otherwise it will skip it.

For example:

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let firstName = "John";
if (firstName !== "") {
  console.log(`Hello, ${firstName}`);
}

// Output: Hello, John

This error is thrown by the JavaScript engine when you try to access a variable that doesn't exist. It has been thrown because the apiUrl variable has not been declared in the current scope. To solve it, you'll need to declare the variable, for example like this:

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let apiUrl = 'http://example.com';
console.log (apiUrl);

For more information, you can read this article.

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const promise = new Promise((resolve, reject) => {
    if (someCondition) {
        resolve('the promise was fulfilled');
    }
    reject('the promse was rejected');
});

Declaring a variable in code typically involves using the keyword const or let before the variable name in most languages, unless declared as a var in JavaScript.

Here's an example of declaring a variable in JavaScript:

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let myVariable = 5;

document.querySelector is used to select a single element from the DOM tree, while document.querySelectorAll is used to select multiple elements from the DOM tree.

For example, in JavaScript:

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// Select the first <div> element
let el = document.querySelector("div"); 

// Select all <div> elements
let els = document.querySelectorAll("div"); 

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if (condition1 && condition2) {
  // execute code
}

The !== operator is a comparison operator in JavaScript which means "not equal and not undefined". It is used to compare two values to see if they are not equal, or if one of the two is undefined.

For example:

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let a = 1;
let b;

if (a !== undefined) {
  console.log("a is defined");
}

if (b !== undefined) {
  console.log("b is defined");
}
// This will print "a is defined" only, as b is undefined

HTML:

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<form>
  <label for="userName">Name: </label>
  <input type="text" name="userName" id="userName" />
  <input type="submit" value="Submit" />
</form>
<h1>Hello</h1>

JavaScript:

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document.querySelector('form').addEventListener('submit', (e) => {
  e.preventDefault();
  const userName = document.querySelector('#userName').value;
  document.querySelector('h1').textContent = `Hello, ${userName}`;
});

To change the text of a button using innerHTML, you can use the following code:

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document.getElementById("myButton").innerHTML="New Text";

More information can be found on MDN's documentation page.

In most programming languages, you can embed a YouTube video into your code using an iframe element with a source URL pointing to the video. For example, in HTML/JavaScript you can use the following code:

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<iframe src="https://www.youtube.com/embed/VIDEO_ID" 
    frameborder="0" allowfullscreen>
</iframe>

Replacing VIDEO_ID with the ID of the video whose embed code is provided on YouTube. For more information, refer to Google's official documentation.

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var city = 'New York';
var country = 'United States';

console.log(`I am from ${city}, ${country}.`);

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function countDecimalPlaces(number) {
  const decimalIndex = number.toString().indexOf('.');
  return decimalIndex >= 0 ? number.toString().length - decimalIndex - 1 : 0;
}

A carousel is a slideshow for cycling through elements, such as images or text. It's also known as a slider or a rotating banner.

You can create a carousel using HTML, CSS, and Vanilla JavaScript, by combining classes along with HTML elements, styling them with CSS, and adding interactive behavior with JavaScript.

You can find various examples online, such as this freeCodeCamp article for a simple carousel.

Here's an example of some HTML, CSS and JavaScript to create a carousel with previous and next buttons:

HTML:

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<div id="slider">
    <div class="slide">1</div>
    <div class="slide">2</div>
    <div class="slide">3</div>
</div>
<button class="prev">Prev</button>
<button class="next">Next</button>

CSS:

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#slider { 
    position: relative;
    width: 300px; 
    margin: 20px auto;
}
.slide {
    position: absolute;
    width: 300px;
    left: 0px;
    top: 0px;
    animation-name:fading;
    animation-duration: 1.5s;
    animation-iteration-count: infinite;
}
@keyframes fading {
    0% { opacity: 0; }
    50% { opacity: 1; }
    100% { opacity: 0; }
}

JavaScript:

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const slides = document.querySelectorAll('.slide');
let index = 0;

function prevSlide(){
    slides[index].classList.remove('active');
    index--;

    if(index < 0)
        index = slides.length -1;

    slides[index].classList.add('active');      
}

document.querySelector('.prev').addEventListener('click', e => {
    prevSlide();
});

function nextSlide(){
    slides[index].classList.remove('active');
    index++;

    if(index > slides.length -1)
        index = 0;

    slides[index].classList.add('active');      
}

document.querySelector('.next').addEventListener('click', e => {
    nextSlide();
});

You can store data in local storage using the localStorage object in JavaScript.

For example, to store an item with key of myKey and value of myValue, you can use the following code:

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localStorage.setItem('myKey', 'myValue');

You can then retrieve the value by using the key like this:

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let myValue = localStorage.getItem('myKey');

For more information, please checkout the MDN localStorage Documentation.

In JavaScript, selectors can be used to select elements in the DOM. A selector can be an element ID, class, or tag name such as document.querySelector('#my-id'). Here is an example of using a selector in JavaScript to select an element with an ID of 'my-id'.

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const element = document.querySelector('#my-id')

More information about selectors in JavaScript can be found in the MDN web docs here.

In JavaScript, you can use a for loop to execute a set of statements a given number of times. For example, this JavaScript for loop prints the numbers 1 - 10:

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for (let i = 1; i <= 10; i++) {
  console.log(i);
}

For a more in-depth explanation of for loops, see this article: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Loops_and_iteration

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let city = 'Toulouse';
let country = 'France';
console.log(`I am from ${city}, in ${country}.`);

This can be done with JavaScript and can be easily achieved using the toLowerCase() method.

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// Select the variable
let userInput = "Something To Convert";

// Convert variable to lowercase
let userInputLower = userInput.toLowerCase();

// Log the conversion
console.log(userInputLower); // prints "something to convert"

You can use the Array.prototype.findIndex() method in JavaScript to find the index of an element with a matching value.

Example code:

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const array1 = [2, 5, 9];

let index = array1.findIndex(x => x == 5); 

console.log(index); // 1

More information on the Array.prototype.findIndex() method can be found here.

JavaScript events are triggers that initiate the execution of JavaScript code when a certain action occurs. Examples of actions that can trigger events include clicking a button, pressing a key, scrolling the page, hovering over an element, and submitting a form.

For example, when a user clicks a button, a click event is triggered. A keypress event is triggered when a user presses a key. Other events such as scroll, mousemove, focus, and blur, are also triggered when a user interacts with a web page.

In order to use JavaScript events, you must define a function in the code that will be executed when the event action occurs. This is known as an event handler. Some common JavaScript events and their event handlers include onclick, onchange, onkeypress, onmouseover, onsubmit, onfocus, and onblur. For example, to run a function when a user clicks a button, you would use the onclick event handler.

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document.getElementById("myButton").onclick = myFunction;

function myFunction() {
  console.log("The button was clicked!");
}

HTML:

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<div class="background-image-container"></div>

CSS:

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.background-image-container {
  background-image: url('background-image-url.jpg');
}

JavaScript:

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let hour = new Date().getHours();
const backgroundImageContainer = document.querySelector('.background-image-container');

if (hour > 18) {
  backgroundImageContainer.style.backgroundImage = 'url("background-image-url-after-18.jpg")';
}

The first steps with coding involve learning a programming language and deciding what you are going to code. Depending on your goals, you can learn a language like JavaScript, HTML, or Python. Here is a helpful guide to choosing a programming language: https://www.w3schools.com/whatis/ Then, you can try following a tutorial or creating your own project.

Learning coding can take a lot of time for several reasons. First, becoming fluent in a particular coding language often requires extensive practice in order to master. Additionally, as coding languages are constantly evolving and new libraries and frameworks are being released, staying up-to-date with current coding trends requires investing time in study and practice. Fortunately, many resources are available such as online tutorials and bootcamps to help speed up the process.