JavaScript skills are in high demand in the tech industry. As a JavaScript developer, you'll find abundant job opportunities with competitive salaries. Familiarizing yourself with these commonly asked JavaScript interview questions and answers can help you prepare and increase your chances of success in the interview process. Have a look!
If you are going to attend a JavaScript interview, then it is a must for you to get a complete knowledge of JavaScript and what type of questions will be asked commonly in the JavaScript interview. In this blog, I have come up with the most frequently asked JavaScript interview questions and answers. Refer to these questions and answers to crack an interview in the very first attempt.
Below mentioned are the Top JavaScript Interview Questions and Answers that will help you to prepare for the JavaScript interview. Let's have a look at them.
Categories of Javascript Interview Questions - 2024 |
JavaScript is a scripting language used for programming web pages as well as server systems. It is an object-oriented, interpreted, lightweight, and powerful programming language made up of first-class functions. JavaScript can update the content dynamically for web pages.
Java is an object-oriented and structured programming language, which helps to run web pages on different platforms. The java code should be compiled on the compiler. JavaScript is an object-oriented scripting language. In which, the scripts are optimized for both server and client-side. Javascript is introduced to perform HTML pages.
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JavaScript data are of the following types -
Top 10 Programming Languages that you need to watch out to boost your career in 2021
A global variable is a special kind of variable in JavaScript. This variable is easy to use and also available across the entire length of the JavaScript code. Mainly, the var keyword is used to declare a global or local variable.
Related Article: Types of JavaScript Variables |
The Input provided by any user in JavaScript is entered with the help of a prompt box. While putting forward the data or the input, the prompt box allows the user to do this with the help of a text box. To include the number, a label box is also used.
There are two basic groups of data types -
Even though global variables are easy to use, these have some shortfalls. While using this type of variable, the problem of clashing the variable names of different global and local scope occurs. The code that is often relied on the global variable also gets difficult to be tested and debugged.
Netscape company had developed the JavaScript Programming Language.
We use object data type variables in JavaScript.
If no value has been given to the variable then, it is called a null object (or) null value.
Navigator. platform String property is used to detect issues of the operating system in a cloud.
The popups available in JavaScript are Alert, Prompt, and Confirm.
Both null and undefined have an empty value, but the difference between these two is:
Two ways are available to read and write a file, they are:
Arrays are used to store various values in a single variable.
Defining an array in JavaScript:
var mobile = [“Oppo”, “ Samsung”, “Vivo”]
By using a new keyword:
Var mobile = new array(“ Oppo”, “Samsung'', “Vivo”)
There are two types of functions that are supported by JavaScript. They are -
“This” keyword is an object in a javascript, where it refers to. It has different values at different stages, whereas in method “this” is used as an owner object and in function, it is called a global object.
In JavaScript, we can submit a form by using
document.form[0].submit();
Automatic type conversion is supported by javascript and usually, the developers of javascript use the automatic type conversion method.
As JavaScript is an object-oriented scripting language, it is very easy to create objects in JavaScript.
var std = { name: “ David”, age: 16, id: 364 };
JavaScript variables have different scopes. The scope of the variable is nothing but the functionality of the variable.
The named function in JavaScript defines the name as well as the value of a function. It is defined by using the keyword
"function”
function named()
{
// write code
}
The JavaScript variable represents the arguments that can be passed to the function. By using, ‘type of’ operator we can represent the argument objects.
Example:
function fun(a)
{
console.log(typrof a, arguments.length);
}
fun(7);
fun( "2", "3”, "4");
fun();
The callback is a typical function of JavaScript that can be passed as an option or argument of JavaScript. Sometimes, callbacks can also be termed simple events. Users are given calls to react to different kinds of triggered situations.
Different types of errors in JavaScript are:
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By using the method Document.getElementsByclass name(), we can get elements in the class name.
The closure is a primary mechanism to private the data items. Closures give access to the outer function’s scope from the inner function's scope. Closures are created for every function in JavaScript. To define a closure, create a function inside another function to expose it.
“===” is a strict equality operator, that returns a true value, if the two operands have the same value.
Using dot(.) notation we can read and write the properties of JS.
There are three possible ways to declare a variable in JavaScript are:
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A NAN (not a number) method is used to return a true value if the variable has no number.
function number(num)
{
if(isNaN(num))
{
returns if it is not a number;
}
return if it is a number;
}
Let us consider an array
Var array = [ “1”, “2”, “3,'' “4” ];
We consider four methods to empty an array
1. array = []
2. array.length = 0;
3. array.splice(0, array.length);
4. while (array.length)
{
array.pop();
}
The type of operator is basically just the unary operator that is used before the single operand. The value indicates the operand's data type. The type includes Boolean, number, and string.
MUL is a multiplication function. The multiplication of numbers can be done as a value is defined in the function and the value is returned by another function and the process goes on.
Example:
function mul(a)
{
return function(b)
{
return function(c)
{
return a*b*c;
};
};
}
Redirection of the page is possible in JavaScript. By using two ways we can redirect a page to other pages, they are:
window.location.href = (“http//jaquar.com”);
window.location.href = (“http//jaquar.com”);
By using,object.property_name The = value we can add a property to the JS object
By using, deleteobject.property_name is used to remove the property from the JS object.
We can validate a variable by using the following script
<script>
function validateform()
{
var fullname = document.firstform.fullname.val;
var pwd = document.pwd.val;
if(fullname==null || fullname=="")
{
alert("fullname should be filled")
return true;
}
else if(password.length<5)
alert("pwd must me upto 5 characters long"):
return false;
}
}
</script>
<body>
<form name =" firstform" method= "post" action ="xyz.jpg" onsubmit =" return validateform()">
fullname = input type= "text" fullname ="name">
<br/>
pwd = inputtype="pwd" name="pw">
<br/>
<inputtype="submit"value"register">
</body>
</form>
Date object in JavaScript helps to get information about the day, month, and year. By using the date object we can set the timer on the screen.
function display()
{
var date = new date();
var day = date.getday();
var month= date.getmonth()+1;
Var year = date.getyear();
doc.write("date is: "+day+"/"+month+"/"+year+");
}
display();
Debugger keyword in JavaScript helps in setting a breakpoint in the code itself. The program will stop executing code where the debugger keyword is applied in the program.
function display()
{
a = 10;
b = 20;
c = a+b;
debugger;
doc.write(c);
doc.write(a);
}
display();
Weakmap is similar to a collection of objects like a map. If the weak map object is set to a process, it considers each element as a key object and that key object will have a weak reference.
function display()
{
var wm = new WeakMap();
var object1 = {};
var object2 = {};
var object3 = {};
wm.set(object1, "AngularJS");
wm.set(object2, "ReactJS");
wm.set(object3, "VueJS");
doc.writeIn(wm.has(object3));
}
display();
The applications written in JavaScript are known as JavaScript frameworks. These frameworks are different forms of JavaScript libraries and flows. Here is a list of some important frameworks, they are:
Related Article: Best JavaScript Frameworks |
Espace characters are used to handle the special characters without breaking the code in javascript. It uses a black slash for different characters like single and double quotes, newline, and so on
Number objects help to represent the number of values to the variables. The values may be floating-point or integer. In JavaScript, the floating points are represented by using the IEEE standard.
function display()
{
var a = 10;
var b = 0.7;
var c = 11d5;
doc.write(a+" "+b+" "+c+");
}
display();
Set objects are used to store different values to the elements. The values may be a reference or primitive values.
function display()
{
var set = new Set();
set.add( "Angular JS":;
set.add(" Vue");
set.add("React JS);
for(set the elements of set)
{
doc.writeIn(elements):
}
}
display();
Fibonacci series is a series of numbers, in which every value is the sum of the preceding two numbers starting with 0 and 1.
Example - 0,1,1,2,3,5,8,13,21,34……..
function fibonacci(n);
{
var x=o, y=1;
for (var i=0; i < n; i++);
{
var temp = x+y;
x = y;
y = temp;
}
return x;
}
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Ravindra Savaram is a Technical Lead at Mindmajix.com. His passion lies in writing articles on the most popular IT platforms including Machine learning, DevOps, Data Science, Artificial Intelligence, RPA, Deep Learning, and so on. You can stay up to date on all these technologies by following him on LinkedIn and Twitter.