document.querySelectorAll is a method in JavaScript used to select a group of elements in the Document Object Model (DOM) based on a CSS selector. It returns a static NodeList containing all elements that match the specified selector. It is useful for manipulating multiple elements at a time.

For example, if you wanted to change the background colour of every element with a particular class in your HTML, you could do something like this:

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let elementList = document.querySelectorAll('.my-class');

for (let element of elementList) {
  element.style.backgroundColor = '#F00';
}

Removing items from a JavaScript array is often referred to as 'splicing'.

To remove an item from an array in JavaScript, use the splice() method. splice() takes two parameters, one for the index of the item to be deleted and one for the number of items to be deleted. For example, to remove the third item from an array, arr, we can do:

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 arr.splice(2, 1);

Where 2 is the index and 1 is the number of items to remove, i.e., one item in this case.

This method will return an array containing the deleted items. To simply delete without returning the deleted items, pass 0 as the second argument (number of items to be deleted).

More information can be found on the MDN Web Docs.

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.

In JavaScript, you can use an array literal to store multiple values in a single variable. Array literals use square brackets and their elements are separated by commas. For example:

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let days = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday'];

You can also create an array using the Array constructor. The syntax is:

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let arr = new Array(element0, element1, ...);

For example:

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let numbers = new Array(1, 2, 3, 4, 5);

Learn more in the Mozilla Developer Network guide to JavaScript Arrays.

This can be accomplished with a few lines of HTML and JavaScript. Here is an example HTML button that redirects to a YouTube video when clicked:

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<a href="https://www.youtube.com/watch?v=YOUTUBEVIDEOID" target="_blank">
   <button>Go to YouTube Video</button>
</a>

The YOUTUBEVIDEOID should be replaced with the actual video ID that is specified in the YouTube video URL.

Once the button is clicked, the page will be redirected to the YouTube video.

For more information, you can reference this article.

The ISO 8601 standard for describing dates and times is widely used in applications, and JavaScript provides built-in support for working with it. The toISOString() method of the Date object can be used to convert the current date into an ISO 8601 string in the format YYYY-MM-DDTHH:mm:ss.sssZ, which is the same as RFC3339.

Here's an example in JavaScript:

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const date = new Date('2021-02-23 13:11:07');
const isoString = date.toISOString();
console.log(isoString); // 2021-02-23T13:11:07.000Z

To set a JavaScript attribute, you need to use the setAttribute() method. The setAttribute() method accepts two parameters, an attribute and its value. The attribute should be provided as a string and its value can be provided as a string, number, boolean, or any other type.

Here's an example for setting an HTML element's className attribute using setAttribute():

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<div id="example"></div>

// Set the className attribute
document.getElementById("example").setAttribute("className", "my-class");

More information on setAttribute() can be found in the MDN Web Docs.

The Math.max() method returns the largest of zero or more numbers. The syntax for using Math.max() is:

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Math.max(value1, value2 [,value3, ...])

You can also use it to find the maximum of an array. To do so, you would use the apply() method:

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Math.max.apply(null, [value1, value2, value3, ...]);

Here is a full example showing how to use Math.max() with an array:

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const numbers = [1, 12, 4, 18, 9];

const maxValue = Math.max.apply(null, numbers);

console.log(maxValue); // output: 18

Reference:

• JavaScript Math.max()

Math.abs is a method in JavaScript that returns the absolute value of a number.

To use it, you simply pass in the number that you want to find the absolute value of.

For example:

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let x = Math.abs(-3);
console.log(x); // 3 

document.querySelector() is a method in JavaScript that is used to query a document for an element and return the first element within the document that matches the specified selector or group of selectors. It returns the element object if there is a match, or null if there is no match. Generally, it is used to select a single element from a document, similar to how getElementById() works but more powerful. For example, the following code selects the first <p> element in the document:

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let firstParagraph = document.querySelector('p');

Reference: MDN

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, you can create a code that says "I love you" every time the user clicks on anywhere on the page by attaching an event listener to the document object:

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document.addEventListener('click', function(){
    alert('I love you');
});

Here, we attach an event listener to the document object using addEventListener. We define the type of event as click and the function that is executed whenever the click event occurs is alert('I love you').

For more information on how to use the addEventListener, please refer to this tidy guide by W3Schools.

A URL parameter is a set of characters added to the end of a URL that send data to a website or web application. In the URL, a parameter is defined by the symbol “?”, followed by a key-value pair, and separated by the symbol “&”. For example:

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example.com?parameter1=value1&parameter2=value2

In this example, parameter1 is equal to value1, and parameter2 is equal to value2.

URL parameters are commonly used to send information from a web page to another. For instance, a website may send parameters to display a specific page, or to pass user information from page to page.

More information about URL parameters can be found here.

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.

Java and Javascript are two very different programming languages. Java is an object-oriented, class-based, general-purpose programming language while Javascript is a prototype-based scripting language. Java is compiled into bytecode, which then runs on a virtual machine or browser, while JavaScript is an interpreted language run directly inside a web browser. Java is strongly typed, which means it requires variables to be declared before use, whereas JavaScript is a loosely typed language which allows for variables to be changed more freely.

In Javascript, you can make a prompt case-insensitive by using the String.prototype.toLowerCase method. For example:

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let input = prompt("Please enter value");
let cInput = input.toLowerCase();

The first line asks for user input and stores the result in input, then the second line stores the user answer in cInput, after being changed from any case type to lowerCase.

More information on the toLowerCase method can be found here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/toLowerCase

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

In most programming languages, you can allow both capital and lowercase spellings by using the .lower() or .upper() methods.

For example, in JavaScript you can use .toLowerCase() or .toUpperCase() methods to convert strings to either all lowercase or all uppercase characters.

For example:

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let name = 'Hermione';
let upperName = name.toUpperCase(); //HERMIONE
let lowerName = name.toLowerCase(); //hermione

References:

• MDN Web Docs - String.prototype.toLowerCase()
• MDN Web Docs - String.prototype.toUpperCase()

Using JavaScript, you can create a prompt question in which the user's input must both contain a capital letter and a lowercase letter. This can be achieved by using a Regular Expression within an if statement to ensure that the user's input matches the specific RegEx pattern you're looking for.

The following code example shows how this could be done:

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let answer = prompt("Please enter username");
const regex = /^(?=.*[a-z])(?=.*[A-Z])[a-zA-Z]+$/;

if (regex.test(answer)) {
  alert("Valid input! Thank you.");
} else {
  alert("Input must contain both capital and lowercase letters!");
}

For more information on Regular Expressions, please check out this guide.

You can create a prompt question with different spelling answers in most modern coding languages. A common example using JavaScript would be using the prompt() function to ask the user a question, followed by the if...else command to determine whether their response is spelled correctly. For example:

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let answer = prompt('What do you call a group of lions?');

if (answer === 'pride') {
  alert('You got it right!');
} else {
  alert('The correct spelling is "pride"');
}

That way, if the user spells the answer incorrectly, the if...else statement will alert them.

More information on prompt() and if...else statements can be found here:

• prompt()
• if...else

In JavaScript, you could use a ternary operator to create a prompt with different spellings. A ternary operator is an expression that takes three operands and evaluates the expression depending on a boolean evaluation of the first operand.

In the below example, the first operand is a prompt used to ask the user to select whether they have either "apple" or "Apples". The second operand is the value on the left side of the colon, which is a prompt with the spelling "apple". The third operand is the value on the right side of the colon, which is a prompt with the spelling "Apples".

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var selection = prompt("Do you have Apple or Apples?") == "apple"? "apple": "Apples";

The example is taken from this article.

Arrays and objects are both used to store collections of data in JavaScript. The main difference between them is how they store data. Arrays store data in consecutive memory locations, and objects store data in named key-value pairs.

For example, an array of numbers can be declared using square brackets [1,2,3], whereas an object would use curly brackets {"a": 1, "b": 2, "c": 3}.

Read more about the difference between arrays and objects in JavaScript here.

In most programming languages, you can delete an item from an array using the splice() method. The splice() method takes two arguments, the starting index (the position of the item) and the number of items you want to delete (usually 1). For example, if you want to delete the item in index 3 of an array myArray, you can use the code shown below:

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myArray.splice(3,1);

For more information, check out this page from W3Schools: Array.prototype.splice().