Whether you are a novice in the software industry or an experienced professional, knowing about computer programming languages always helps you immensely.
One such powerful and flexible programming language of the web which powers the dynamic behaviour on most websites is called Javascript.
Often abbreviated as JS, Javascript is a high-level, interpreted programming language that is an essential part of web applications. Along with HTML and CSS, JavaScript is one of the three core technologies of the World Wide Web.
With multiple usages and applications of JS, it has been the most desired skill set in the industry lately. And thus, many interviewers seek for candidates who are well versed with Javascript.
This is why we have thought to come up with some hot favourite interview questions on Javascript. The questions range from a basic to a mid-senior experience level.
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Moreover, the questions below are collected from several websites as well as from personal interview experiences.
Experience level : 0 to 3 years
Java, on one hand, is a complete programming language whereas, JavaScript is a coded program that can be introduced to HTML pages.
These two languages are not interdependent and are designed for different intent. Also, Java is an object-oriented programming (OOPS) or structured programming languages like C++ or C and JavaScript is a client-side scripting language.
The JavaScript Data types are as follows:
The answer to the second question is No.
Attributes, on one hand, are something that can give more details on an element like id, type, value etc, and on the other hand property is the value assigned to the property like type="text", value='Name' etc.
ECMAScript stands for European Computer Manufacturers AssociationScript.
It is a specification for the scripting language standards.
It has standardized Javascript which made Javascript the best implementation of ECMAScript.
Some of the features of JavaScript are:
The types of function are:
For Example:
function display()
{
document.writeln("Named Function");
}
display();
For Example:
var display=function()
{
document.writeln("Anonymous Function");
}
display();
The Javascript code can be involved in 3 ways
(i) Inline
(ii) Internal
(iii) External
There are three possible ways of defining a variable in Javascript
(i) var (which is used from the beginning)
(ii) const
(iii) let.
The last two ways are the latest ways of defining a variable and are introduced in the ES-2015(ES6 version).
You can say JScript is the same as JavaScript, but Microsoft provides it as Netscape provided the JavaScript language but Microsoft changed the name and called it JScript to avoid the trademark issue.
A simple example of JavaScript hello world is given below.
You have to place it inside the body tag of HTML.
<script type="text/javascript">
document.write("JavaScript Hello World!");
</script>
In JavaScript, we need closures when a variable which is defined outside the scope in reference is accessed from some inner scope.
var num = 10;
function sum()
{
document.writeln(num+num);
}
sum();
console.log(mul(2)(3)(4)); // output : 24
console.log(mul(4)(3)(4)); // output : 48
function mul (x)
{
return function (y)
{ // anonymous function
return function (z)
{ // anonymous function
return x * y * z;
};
};
}
The mul function accepts the first argument and returns an anonymous function, which takes the second parameter and returns another anonymous function that will take the third parameter and return the multiplication of the arguments that have been passed.
We know that JavaScript, a function defined inside another one has access to the outer function's variables. Therefore, when a function is a first-class object it can be returned by other functions as well and be passed as an argument in another function.
An anonymous function can be defined in a similar way as a normal function. It would not have any name.
REST stands for Representational State Transfer.
It is an architectural style that has largely been adopted as a best practice for building web and mobile applications.
RESTful services are designed to be lightweight, easy to maintain, and scalable and are typically based on the HTTP protocol, make explicit use of HTTP methods (GET, POST, PUT, DELETE), are stateless, use intuitive URIs, and transfer XML/JSON data between the server and the client.
Undefined value means the
Void(0) is used to prevent the page from refreshing.
Parameter "zero" is passed while calling.
Void(0) is used to call another method without refreshing the page.
In two-way data binding, changes to the UI and changes to the model occur asynchronously—a change on one end is reflected on the other. In one-way data binding, data only flows one way, and any changes that the user makes to the view will not be reflected in the model until the two are synced. Angular makes implementing two-way binding a snap, whereas React would be your framework of choice for deterministic one-way data flow.
If you use innerHTML in JavaScript the disadvantage is
The push method is used to add or append one or more elements to the end of an Array. Using this method, we can append multiple elements by passing multiple arguments
concat() method returns the character at the specified index.
The arguments object has a callee property, which refers to the function you're inside of. For example −
function func() {
return arguments.callee;
}
func(); // ==> func
Additional Questions:
There might be few questions like,
For such type of questions, you need to have a strong command over Javascript and its syntax. Always try to first understand the problem statement and then focus on the output.
Go through the past assignments you have done with the subject and make sure you are able to speak confidently on them. If you are fresher then interviewer does not expect you will answer very complex questions, rather you have to make your basics concepts very strong.
Here's another useful article for you, if you are Getting Ready For An Interview After Career Break.