JavaScript Interview Questions
1 .
If you need to calculate the Fibonacci series in JS, what will you do?
Fibonacci series is a pattern in which each given value is the sum of the previous two, and it starts with 0,1.

Method :

* use function fib(n),
* Declare var a=0 and b=1
* Use this condition (var i=0; i<n; i++)
* Use var temp = a+b;
* Next make a=b
* And b=temp;
* }
* Return a;

The series will come like 0,1,1,2,3,5…
2 .
In JavaScript, append a new element at the end of the array.
To append an element in a JavaScript array, we use `push()`, and to remove an `array, pop()` is used.

Syntax :
``array.push(item1, item2, …, itemX)``
3 .
How do we add/remove properties to objects dynamically in JS?
We can add a property to an object by using :
``object.property_name =value``
To delete a property, we can use :
``object.property_name``
Example :

``````   let user = new Object();

user.name=’ftl’;

user.age  =22;

console.log(user);

delete user.age;``````
4 .
What is the procedure to merge two arrays?
Syntax :

``````var arr1 = [1,2,3]
var arr2 = [4,5,6,7]
var mergedArrays = […arr1, …arr2]
document.write(‘Merged arrays’, mergedArrays)``````
5 .
What is Means by Currying in Javascript?
Currying is a method of evaluating the function with many arguments, into a sequence of function with a single argument. Currying helps you to avoid spending the same variable again and again. It helps to create a larger order function
6 .
How does inheritance work in JavaScript?
When it comes to inheritance, JavaScript simply has one construct: objects. Each object has a separate property which operates a link to another object called its model. That prototype object has a prototype of its individual, and so on until an object is terminated with null as its prototype.
7 .
Why do we use onabort event in JavaScript?
The onabort event is executed when the loading of an image is aborted. Use it in an image tag like this:

``<img src="demo_image.jpg" onabort="display()">``

``````function abortFunc()
{
}``````
8 .
What are logical errors in JavaScript?
Logic errors occur when there is a mistake in the logic. This can lead your script to work inappropriately to give unexpected results.
9 .
Which event triggers in JavaScript when an object loses focus?
The blur event triggers when object loses focus. An example here displays that we write a name in the textbox and then when the object loses focus, the text color is changed. This happens since the blur event triggers when the focus ends:

``````<!DOCTYPE html>
<html>
<body>
<h2>Testing</h2>
<input type="text" onblur="display(this)">
<script>
function display(z) {
z.style.color = "green";
}
</script>
</body>
</html> ``````
10 .
What is the usage of `onpagehide` event in JavaScript?
When a visitor leaves the web page, then the `onpagehide` event triggers. The visitor can move to another page or click a link after leaving the current web page. An example here displays an alert box when the user tries to leave the page. This happens since `onpagehide` event fires when the page is left :

``````<!DOCTYPE html>
<html>
<body onpagehide="display()">
<p>Close the page</p>
<script>
function display() {
alert("It was nice having you here!");
}
</script>
</body>
</html>``````