##### Unknown “non-finite double value” Javascript error being thrown

The “non-finite double value” error is typically thrown when JavaScript encounters a value that is not a finite number, such as NaN (Not-a-Number) or Infinity. This can happen when an operation or function returns an unexpected result, such as dividing by zero or trying to square root of a negative number.

Here are a few common causes of this error:

1. Attempting to divide by zero: `var x = 1 / 0; // throws "non-finite double value" error`
2. Attempting to take the square root of a negative number: `var x = Math.sqrt(-1); // throws "non-finite double value" error`
3. Using the `parseFloat()` function to convert a non-numeric string to a number: `var x = parseFloat("hello"); // throws "non-finite double value" error`
4. Using an undefined or null variable as an operand in a mathematical operation: `var x; x = x + 1; // throws "non-finite double value" error`
5. Using an object that is not a number in a mathematical operation: `var x = {}; x = x + 1; // throws "non-finite double value" error`
6. Trying to use a function or object that is not a number in a mathematical operation.

To troubleshoot this error, you can try the following:

1. Check your code for any operations that could result in a non-finite number, such as dividing by zero or trying to take the square root of a negative number.
2. Check your code for any places where you are using the `parseFloat()` function to convert non-numeric strings to numbers.
3. Check your code for any places where you are using undefined or null variables as operands in mathematical operations.
4. Check your code for any places where you are using objects that are not numbers in mathematical operations.
5. Check your code for any places where you are trying to use a function or object that is not a number in a mathematical operation.

By isolating the specific line of code or operation that is causing the issue, you should be able to better understand the problem and find an appropriate solution. ##### Detecting an undefined object property

In JavaScript, you can use the `typeof` operator to check if an object property is defined. The `typeof` operator returns the type of a variable or expression. If the property is defined, the `typeof` operator will return the type of the property (e.g. “string”, “number”, “object”, etc.). If the property is not defined, the `typeof` operator will return “undefined”. Here’s an example

``````let obj = {
name: "John"
};

if (typeof obj.age === "undefined") {
console.log("The 'age' property is not defined.");
}``````

Another way of detect an undefined property on an object is using the `in` operator. This operator checks if an object has a property with a given name. You can check if an object property is undefined or not by checking if the property is in the object or not. Like this:

``````let obj = {
name: "John"
};

if (!('age' in obj)) {
console.log("The 'age' property is not defined.");
}``````

You can also use the `hasOwnProperty()` method, it checks if an object has the specified property as its own property, not inherited from its prototype

``````let obj = {
name: "John"
};

if (!obj.hasOwnProperty('age')) {
console.log("The 'age' property is not defined.");
}``````

It is important to note that `undefined` values are different from `null` values, so if you want to check if a property has a null value, you should use strict equality operator `===` to check it.

``````let obj = {
name: "John",
age: null
};

if (obj.age === null) {
console.log("The 'age' property is null");
}
``````

It’s important to notice that if the property does not exist on the object and you use the `obj.property` notation it will return `undefined`, but if the object doesn’t exist at all, trying to access its properties will cause a ReferenceError. ##### How do I check if an array includes a value in JavaScript?

In JavaScript, you can use the `Array.prototype.includes()` method to check if an array includes a specific value.

Here’s an example of how you can use the `includes()` method to check if an array of numbers includes the number 42:

``````var numbers = [1, 2, 3, 42, 5];
console.log(numbers.includes(42));  // output: true
``````

The `includes()` method returns a boolean value indicating whether the specified value is found in the array. In the above example, since 42 is present in the array the output is `true`.

You can also check if the array includes an object in the array

``````var people = [{name:'John',age:40}, {name:'Mike',age:25}, {name:'Bob',age:35}];
console.log(people.includes({name:'Bob',age:35}));  // output: false``````

It will return `false` because it compares object reference not the object values.

In this case, you can use Array.prototype.find() method to find the desired object by key-value match

``console.log(people.find(person => person.name === 'Bob' && person.age === 35));``

This method returns the first element in the array that satisfies the provided testing function; otherwise, undefined is returned.

You can also use `indexOf()` method to check if a value exists in an array or not.

``console.log(people.indexOf({name:'Bob',age:35}) != -1)``

It returns the first index at which a given element can be found in the array, or -1 if it is not present. ##### Get the current URL with JavaScript?

You can use the `window.location` object in JavaScript to get the current URL of a web page. The `location` object is a property of the `window` object and contains information about the current URL.

Here’s an example of how you can use it to get the current URL:

``````var currentUrl = window.location.href;
console.log(currentUrl);``````

This will return the entire URL of the current page, including the protocol (e.g. “http” or “https”), the domain, and any query parameters or hash fragment.

`location.origin` will only give the protocol and the domain.

``````var originUrl = window.location.origin;
console.log(originUrl);``````

You can also use `location.pathname` to get only the path of the current page

``````var pathUrl = window.location.pathname;
console.log(pathUrl);``````

You can use `location.search` to get any query parameters in the current page

``````var searchUrl = window.location.search;
console.log(searchUrl);``````

It’s important to note that the `location` object is a read-only object, meaning you can’t use it to change the current URL of a page. If you need to change the URL, you can use the `window.location` object’s `assign()` method to load a new URL or the `replace()` method to replace the current URL in the browser’s history. ##### How can I remove a specific item from an array?

There are a few ways to remove a specific item from an array in JavaScript. Here are a few methods that you can use:

1. The `Array.prototype.splice()` method can be used to remove an item from an array by specifying the index of the item and the number of items to remove. Here is an example of how you can use `splice()` to remove the item at index 2 from an array:
``````var numbers = [1, 2, 3, 4, 5];
numbers.splice(2, 1);
console.log(numbers); // output: [1, 2, 4, 5]``````
1. The `Array.prototype.filter()` method can be used to create a new array with all elements that pass the test implemented by the provided function. Here’s an example of how you can use filter to remove a specific number from an array:
``````var numbers = [1, 2, 3, 4, 5];
numbers = numbers.filter(function(num) { return num !== 3 });
console.log(numbers); // output: [1, 2, 4, 5]
``````
1. You can use `Array.prototype.indexOf()` method to find the index of the desired item and then use `Array.prototype.slice()` to remove that element.
``````var numbers = [1, 2, 3, 4, 5];
var index = numbers.indexOf(3);
if (index > -1) {
numbers = numbers.slice(0, index).concat(numbers.slice(index + 1));
}
console.log(numbers); // output: [1, 2, 4, 5]
``````
1. You can also use the `Array.prototype.findIndex()` to find the index of the item and `Array.prototype.splice()` to remove the specific item.

``````var numbers = [1, 2, 3, 4, 5];
var index = numbers.findIndex(num => num === 3);
if (index !== -1) numbers.splice(index, 1);
console.log(numbers); // output: [1, 2, 4, 5]
``````

All of the above methods will remove the specific item from the array, and return the modified array.

It’s important to note that the `splice()` method modifies the original array, while filter and slice returns new array.

Also, if you are trying to remove multiple elements from an array, you can use these methods multiple times or use nested looping to remove those elements. ##### How do I remove a property from a JavaScript object?

To delete a property from a JavaScript object, you can use the `delete` operator.

For example:

``````let obj = {
key1: 'value1',
key2: 'value2'
};

delete obj.key1;

console.log(obj);  // { key2: 'value2' }``````

This will remove the `key1` property from the `obj` object.

Note that the `delete` operator only works on own properties of an object, and not on properties inherited from the object’s prototype.

If you want to remove a property from an object and all of its prototypes, you can use the `delete` operator in combination with the `in` operator, like this:

``````let obj = {
key1: 'value1'
};

let obj2 = Object.create(obj);

delete obj2.key1;  // This will delete the property from obj2, but not from obj

console.log(obj2.key1);  // undefined
console.log(obj.key1);   // 'value1'

delete obj2.key1 in obj;  // This will delete the property from obj and all of its prototypes

console.log(obj2.key1);  // undefined
console.log(obj.key1);   // undefined`````` ##### How do I get the current date in JavaScript?

There are a few ways to get the current date in JavaScript, depending on what you’re trying to do.

The simplest way is to use the `Date` object, which is built into JavaScript. Here’s an example of how you can use it to create a new `Date` object representing the current date and time:

``````var currentDate = new Date();
console.log(currentDate);``````

You can also pass in a date string to create a `Date` object representing a specific date. For example:

``````var birthday = new Date("January 1, 1990");
console.log(birthday);``````

If you want to format the date in a specific way, you can use the various methods provided by the `Date` object.

Here’s an example of how you can use the `toDateString()` method to format the date as a string:

``````var currentDate = new Date();
console.log(currentDate.toDateString());
``````

which will output date in string form : `Mon Jan 10 2022`

You can also use other methods like `toUTCString()` or `toISOString()` to format the date and time in a specific way.

You can also use `getDate()`,`getMonth()` and `getFullYear()` method to get day, month and year respectively

``````var currentDate = new Date();
console.log(currentDate.getDate());
console.log(currentDate.getMonth());
console.log(currentDate.getFullYear());
``````

Keep in mind that the `Date` object is based on the number of milliseconds that have passed since January 1, 1970, so the output of the `Date` object may be affected by time zone differences. ##### How can I remove an array element by index,using javaScript?

In JavaScript, you can use the `Array.prototype.splice()` method to remove an element from an array by specifying the index of the element and the number of elements to remove.

Here’s an example of how you can use the `splice()` method to remove the element at index 2 from an array:

``````var numbers = [1, 2, 3, 4, 5];
numbers.splice(2, 1);
console.log(numbers); // output: [1, 2, 4, 5]``````

The first argument passed to the `splice()` method is the index of the element to remove and the second argument is the number of elements to remove. In the above example, we are removing 1 element starting from the index 2.

You can also remove more than one element by passing a higher number as the second argument to the `splice()` method:

``````var numbers = [1, 2, 3, 4, 5,6,7,8];
numbers.splice(2, 3);
console.log(numbers); // output: [1, 2, 7, 8]``````

Here we are removing 3 element starting from the index 2.

It’s important to note that the `splice()` method modifies the original array, so after you call the `splice()` method, the element at the specified index will be removed and the remaining elements will be shifted to the left.

You can also use spread operator with `slice()` method to remove an array element by index.

``````let numbers = [1, 2, 3, 4, 5];
let index = 2;
numbers = [...numbers.slice(0,index), ...numbers.slice(index + 1)];
console.log(numbers); // output: [1, 2, 4, 5]
``````

It will return new array without the element in the specified index.

Also be careful when removing elements from an array if you are working with loops, as it can cause the loop to skip some elements or lead to unexpected behavior. ##### What is the difference between “let” and “var”?

In JavaScript, `let` and `var` are both used to declare variables, but they have some important differences in terms of scope and behavior.

• The `var` keyword was used to declare variables before the introduction of `let` and `const` in ECMAScript 6 (ES6). Variables declared with `var` are function-scoped, which means they are only accessible within the function in which they were declared, or if they were declared outside any function, they are accessible throughout the global scope. If a variable is declared with `var` keyword inside a function, it is still accessible throughout the function, even if it’s declared inside an if-statement or for loop, for example.
``````function varFunction() {
if (true) {
var x = 5;
}
console.log(x); // Output: 5
}
varFunction();
console.log(x); // Output: 5``````
• The `let` keyword was introduced in ECMAScript 6 (ES6) as an alternative to `var`, and it is block-scoped. Variables declared with `let` are only accessible within the block in which they were declared.
``````function letFunction() {
if (true) {
let x = 5;
}
console.log(x); // ReferenceError: x is not defined
}
letFunction();
`````` ##### Why let and var bindings behave differently using setTimeout function?

In JavaScript, `setTimeout` is a function that runs a callback function after a specified amount of time has passed. However, the behavior of `var` and `let` bindings can be different when used in conjunction with `setTimeout` due to their different scoping rules.

When a variable is declared with `var` inside a function, it’s accessible throughout the entire function, regardless of whether it’s inside a block or not. This means that when a `setTimeout` callback function is invoked, it has access to the variables declared with `var` in the outer scope.

Here’s an example that shows how `var` behaves with `setTimeout`:

``````function varExample() {
for (var i = 0; i < 3; i++) {
setTimeout(function() {
console.log(i);
}, 0);
}
}
varExample(); // Output: 3 3 3``````

In the above example, the output is 3 three times because by the time the callback function is invoked, the for-loop has already completed and the variable i has the final value of 3.

On the other hand, variables declared with `let` are block-scoped, which means that they’re only accessible within the block in which they were declared. `let` bindings can be captured by closures, so they can be used inside the callback function of `setTimeout` without any problem

``````function letExample() {
for (let i = 0; i < 3; i++) {
setTimeout(function() {
console.log(i);
}, 0);
}
}
letExample(); // Output: 0 1 2``````     