In JavaScript, you can use the .toLowerCase() string method to convert a string to lowercase. For example:

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let message = "SheCodes ROCKS!";
let result = message.toLowerCase(); // result will be "shecodes rocks!"

You can use the following javascript function to calculate age:

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// Function to calculate age (in years)
function calculateAge(dateOfBirth) {
  // Get today's date
  var today = new Date(); 

  // Get the difference (in milliseconds) between the current date and date of birth
  var diffInMilliSeconds = today.getTime() - dateOfBirth.getTime(); 

  // 1 year = 365.25 days
  var diffInYears = diffInMilliSeconds/1000/60/60/24/365.25;

  // Return the difference in years
  return Math.abs(Math.round(diffInYears));
}

Source

You can create an interactive JavaScript application that converts Fahrenheit to Celsius when the element with an id of "p" is clicked. Here is an example of the code for this behavior:

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// Get the element with the id of "p"
let element = document.getElementById('p')

// Set a click listener on the element to run the conversion
element.addEventListener('click', convertFtoC);

// Create the conversion function
function convertFtoC (temperature) {
    let cTemp = (temperature - 32) * (5/9)
    alert(`${temperature} F is equal to ${cTemp} C`)
}

For further reading about this topic, check out this introductory article on JavaScript events.

This indicates that the request failed due to a 401 Authentication error. A 401 error occurs when a request for authentication does not have the Authorization header present or has the invalid credentials.

To fix this, check that:

• the URL being accessed is correct
• the Authorization header being sent contains valid credentials
• the credentials match the expected credentials for the URL

For example, in JavaScript you would need to make sure that the Authorization header is being set in the request like:

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var myHeaders = new Headers();
myHeaders.append("Authorization", "Bearer <Token>");

var requestOptions = {
  method: 'GET',
  headers: myHeaders,
  redirect: 'follow'
};

fetch("url", requestOptions)
  .then(response => response.text())
  .then(result => console.log(result))
  .catch(error => console.log('error', error));

More resources on HTTP Status Code 401:

• https://www.restapitutorial.com/httpstatuscodes.html#401_unauthorized
• https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/401

Cookies can be used in JavaScript to store user information. To use them, you'll first have to create the cookie on the server side and then use the JavaScript document.cookie property to get, set, and delete the cookie.

To set a cookie in JavaScript, you can use the document.cookie property like this:

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document.cookie = "name=value;expires=date";

To get the cookie, use the following code:

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var name = document.cookie.split('=')[0];

To delete the cookie, use the following code:

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document.cookie = "name=; expires=Thu, 01 Jan 1970 00:00:00 UTC";

For more information on how to use cookies in JavaScript, check out this tutorial.

You can create a search form using HTML, JavaScript and PHP. Here’s an example using JavaScript:

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<form>
  <label>Search for a city:</label>
  <input type="text" id="city" />
  <input type="submit" value="Search" onclick="showCityName()" />
</form>

<script> 
  function showCityName() {
    const city = document.getElementById('city').value;
    document.write(city);
  }
</script>

If you’re a beginner, you can use jQuery to create the same form.

Here’s an example using jQuery:

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<form>
  <label>Search for a city:</label>
  <input type="text" id="city" />
  <input type="submit" value="Search" id="loader" />
</form>

<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>
<script> 
  $(document).ready(function() {
    $("#loader").click(function() {
        const city = $("#city").val();
        $("#container").html(city);
    });
  });
</script>

You can find further instructions and resources to help you create this search form here: https://www.w3schools.com/howto/howto_js_trigger_button_enter.asp.

Using the Date object in JavaScript, one can display the country specific time zone time. The toLocaleString method in the Date object can take a second argument which is a options object that can take a timeZone where one can specify the specific time zone.

For example, to display the time zone time for the US East Coast:

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let date = new Date();
let options = {timeZone: 'America/New_York'};
let eastCoastTime = date.toLocaleString('en-US', options);

Check out this MDN page to learn more.

In some programming languages, two exclamation marks before a variable mean "not". It is an operator used to negate the value of a boolean expression i.e. it will evalute the expression to the opposite of its normal truth value.

For example, in JavaScript:

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let a = true;
let b = !!a;
console.log(b); // --> true

In the code example above, the first let statement sets a value of true. Then, the two exclamation marks before the a negates the value, and b is set as true.

To console log a property of an object from an array using JavaScript, you can use the forEach method.

In the example below, we use the forEach method to loop through the array of objects, and then call the console.log method to print the value of the nameproperty from each object.

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const myArray = [
  { name: "Sara", age: 32 },
  { name: "John", age: 21 },
  { name: "Bill", age: 18 },
];

myArray.forEach(function (element) {
  console.log(element.name);
});

The output of this code will be:

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Sara 
John
Bill

This depends on the programming language you are using. In JavaScript, you can use the Math.round() function on the property of an object. For example, if you want to round the x property of an object called myObject, you could do this using the following code.

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myObject.x = Math.round(myObject.x);

More information about the Math.round() function can be found on the MDN web docs.

You can make an HTTP requests in Javascript using the fetch API. An example of a GET request using the fetch API is below:

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fetch('https://example.com/file')
  .then(response => response.json())
  .then(data => console.log(data));

By calling the fetch() function, you can make an API call to any endpoint with an optional configuration object. The .then() functions allow you to manipulate the response and use the response data for further operations.

The following code functions as a date formatter in Javascript:

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function formatDate(date) {
  const daysOfWeek = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'];
  const months = ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December'];

  const dayName = daysOfWeek[date.getDay()];
  const monthName = months[date.getMonth()];
  const day = date.getDate();
  const year = date.getFullYear();

  return `${dayName}, ${monthName} ${day}, ${year}`;
}

And here's an example of how to use it:

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// Output example: Thursday, April 4, 2020
let date = new Date(2020, 4, 4);
let formattedDate = formatDate(date);
console.log(formattedDate);

A loop is a control structure used for repeating a sequence of operations a set number of times. Common types of loops generally exist as for loops, while loops, and do-while loops. In each loop statement, the initialization, termination and increment of a counter variable occurs.

For example, in the JavaScript language, a for loop has the following syntax:

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for (let i = 0; i < N; i++) {
  // Code to execute
}

Here i is the counter variable whose value is initialized to 0; i < N is the Boolean expression that represents our loop termination clause, and i++ is the counter variable's increment.

More information can be found on w3schools.

Removing elements from an array in most programming languages can typically be done with a remove or splice method. For example, in JavaScript, the splice method can be used to remove an element from an array:

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var letters = ["a", "b", "c" , "d"];

letters.splice(2,1);

// letters is now ["a", "b", "d"]

More details about the splice method can be found here.

In JavaScript, to console log each element of an array, you can use a for loop to iterate through the array. The syntax is as follows:

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let array = [element1, element2, element3, ...];
for(let i = 0; i < array.length; i++){
  console.log(array[i]);
}

References:

• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for

To log array elements, you can use a for loop logic. An example of this in JavaScript is shown below:

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let array = ["a", "b", "c", "d"]
for (let i = 0; i < array.length; i++) {
  console.log(array[i])
}

This will log each element of the array to the console.

event.preventDefault() is an important method used in the event handling of webpages. Calling event.preventDefault() will prevent the default behavior of an element from triggering, allowing more control over the flow of an application. For example, if you create a form on your page, calling event.preventDefault() on the form's submission will prevent the page from refreshing, allowing you to handle and process the form without causing the entire page to reload.

You can log the properties of an array to the console with a for loop. Using JavaScript syntax, this could look something like the following:

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const array = [
  {name: 'John', age: 30},
  {name: 'Jane', age: 20}
];

for (let i = 0; i < array.length; i++) {
  console.log(array[i]);
}

This code would log:

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{name: 'John', age: 30}
{name: 'Jane', age: 20}

You can also use the forEach method to iterate over the array and console log the properties.

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const array = [
  {name: 'John', age: 30},
  {name: 'Jane', age: 20}
];

array.forEach(element => {
 console.log(element);
});

Yes, you can add an href attribute to an element within an if statement in JavaScript. Here's an example:

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let someCondition = true;

if (someCondition) {
  let element = document.createElement('a');

  element.innerText = 'Click me';
  element.href = 'https://example.com/';

  document.querySelector('body').appendChild(element);
}

A JavaScript closure is created when a function is defined inside another function. When this happens, the inner function will have access to the variables in the outer function's scope, even after the outer function has returned.

An example of a JavaScript closure is below:

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function outerFunction(x) {
  let outerVariable = x;

  return function innerFunction(y) {
    return outerVariable + y;
  }
}

let myClosure = outerFunction(5);
let result = myClosure(7);
// result = 12

Here, outerFunction defines an outer variable x when declared. When it returns, it returns an inner function that has access to the outerVariable even though outerFunction has already returned and the variable should, by all rights, no longer be accessible.

The Array.prototype.find() function can be used to search for a particular object within an array of objects. The find() method will return the value of the first element within the array that passes the condition specified in the provided callback function. To use this method, it is defined as:

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let result = array.find(function(element) {
  // condition to be satisfied
});

The callback function takes in an argument (element) which is the current element being processed in the array. The element can then be compared against other values, and the condition to satisfy is then defined within this callback function. Once a condition is satisfied, the element that successfully passed the condition is then returned as the output.

For example, if you had an array of objects like this:

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let people = [
  {name: 'John', age: 25},
  {name: 'Mary', age: 18},
  {name: 'Peter', age: 24}
];

You can use the find() method to search for a particular element within the array, in this case, you can search for the object with the name 'John':

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let result = people.find(function(person) {
  return person.name === 'John';
});

console.log(result);
// Output: {name: 'John', age: 25}

The find() function will then search within the people array and return the first element that satisfies the condition of * person.name === 'John'" which in this case, the first element which is the object {name: 'John', age: 25} is returned.

This can be done using JavaScript:

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let milliseconds = Date.now();
setInterval(() => {
  milliseconds = Date.now();
  console.log(`Milliseconds: ${milliseconds}`);
}, 1);

Milliseconds: 1607233758571

Removing items from an array depends on the programming language you are using. For example, in JavaScript you can use .splice() to remove items from an array:

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const myArray = [1,2,3,4];
myArray.splice(2, 1); // remove item with index 2
console.log(myArray); // [1,2,4]

For more specific implementation, you can refer to the documentation for the specific language you are using. For more detailed information, you can check out MDN's page on Array.prototype.splice() and read up on the different arguments you can pass in.

Getters and setters are functions that allow you to get and set object values, respectively. Getter functions return the value of the specified property, while setter functions can set the value of the specified property.

In Javascript, getters and setters are defined using the Object.defineProperty() method:

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let obj = {
    _name: "John Doe"
};

Object.defineProperty(obj, 'name', {
    get: function() {
        return this._name;
    },
    set: function(value) {
        this._name = value;
    }
});

For more information, see MDN - Getters and Setters.

You can use the String.prototype.toLowerCase() in JavaScript to ignore case when comparing user-input.

Take a look at the example below:

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let country = prompt("Where are you from?")

if (country.toLowerCase() == 'brazil' || country.toLowerCase() == 'portugal') {
  console.log('Greetings!');
}

String.prototype.toLowerCase() will convert brazil, Brazil, BRAZIL to brazil so that the comparison of country will match with either brazil or portugal.

References: MDN String.prototype.toLowerCase()