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JavaScript Interview Questions and Answers

Interview Questions December 26, 2018
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JavaScript Interview Questions and answers

JavaScript Interview Questions and answers for beginners and experts. List of frequently asked JavaScript Interview Questions with answers by Besant Technologies. We hope these JavaScript Interview Questions and answers are useful and will help you to get the best job in the networking industry. This JavaScript Interview Questions and answers are prepared by JavaScript Professionals based on MNC Companies’ expectations. Stay tuned we will update New JavaScript Interview questions with Answers Frequently.

Best JavaScript Interview Questions and answers

Besant Technologies supports the students by providing JavaScript Interview Questions and answers for the job placements and job purposes. JavaScript is the leading important course in the present situation because more job openings and the high salary pay for this JavaScript and more related jobs. We provide the JavaScript online training also for all students around the world through the Gangboard medium. These are top JavaScript Interview Questions and answers, prepared by our institute experienced trainers.

JavaScript Interview Questions and answers for the job placements

Here is the list of most frequently asked JavaScript Interview Questions and Answers in technical interviews. These questions and answers are suitable for both freshers and experienced professionals at any level. The questions are for intermediate to somewhat advanced JavaScript professionals, but even if you are just a beginner or fresher you should be able to understand the answers and explanations here we give.

Q1) What is JavaScript?

JavaScript is a client-side as well as a server-side scripting Programming language that can be inserted into HTML pages Code and is understood by web browsers. JavaScript is also an Object-based Programming language.

Q2) What are JavaScript Data Types?
  • String
  • Function
  • Boolean
  • Object
  • Number
  • Undefined
Q3) What is the differentiation between JavaScript and Java?

Main differences between Java and JavaScript: Java is an OOP programming language while JavaScript is an OOP scripting language. Java creates a programming language that run under a virtual machine or browser while JavaScript code is run on a browser only. Java code requires to be compiled while JavaScript code is all in the text.

Q4) What close() makes in Javascript?

This is called a JavaScript closure Current Window. It performs it possible for a function to have “private” variables. The counter is covered by the scope of the unknown function, and can only be modified using the add function. A closure is a function having a path to the parent scope, even after the parent function has finished.

Q5) What is the definition of the prompt box?

The Input given by any user in the JavaScript is listed with the help of a prompt box. While putting forward the data or the input, the prompt box enables the user to do so with the guidance of a text box. To enter the number, label box is also done.

Q6) List some features of JavaScript It is an object-based scripting language.
  • Given to the user more control over the browser.
  • It’s Handling dates and time.
  • It Identifying the user’s browser and OS
  • It is interpreter based scripting language
  • It is one of the case sensitive
  • It’s mostly of the javascript control statements syntax is the same as the syntax of control statements in C language
Q7) List some of the advantages of JavaScript?

Speed: Client-side JavaScript is really powerful Faster because it can be run quickly within the client- side browser.
Simplicity: It is relatively simple to learn and implement.
Popularity: It is used throughout on the web browser. The support to learn JavaScript are numerous.
Interoperability: It’s a plays nicely with other programming languages and can be used in a large variety of applications.
Server Load.: Being the client-side defeats the demand on the website server.
Rich interfaces: Drag and drop components or slider
Extended Functionality: Third-party add-ons similar to Greasemonkey enable JavaScript developers to write snippets of JavaScript which can perform on desired web pages to extend its functionality.
Versatility: Now, there exist many ways to use JavaScript through Node.js servers.

Q8) What are the disadvantages of using inner HTML in JavaScript?
  • The method of using inner HTML is much delayed than the rest of the variables as its content is slowly built into many elects and needs time to get re-parsed.
  • While managing the inner HTML, the content gets replaced in JavaScript.
  • Adding to inner HTML can’t be used correctly.
  • Using inner HTML can also reveal the text of the JavaScript. Since no validation is needed by it, any type of
  • valid inner HTML can be used. Even broken HTML can also be done and this can cause queries.
  • The old content also gets quickly replaced.
Q9) What does a type of operator do?

The operator types of gives the model of a variable/data possible in it. The kind of operator can be used on Reference data types also.

Q10) What are the different scopes of a variable? Define local variable?

A scope is a region from a program. Variable Scope is a region into a performance where a variable is maintained and used. So, we can have three types of scopes depending on the state anywhere those are held and used – Local variables are limited inside a reception or a block. Global variables are outside any functions.

Q11) What is the means by ‘call back’?

The callback is a general function of the JavaScript which can be given as an option or argument of JavaScript. Sometimes, callbacks can also be termed as simple functions. Users are given calls to react to different kind of triggered conditions.

Q12) What does unshift() function do in Javascript?

Push () is inserts elements into an array at the end of it, the unshift () function includes elements at the start of an array.

Q13) 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

Q14) What are Cookies in Javascript?

A Cookie is a store the variable on a client’s/visitors machine. Managing Cookies, the servers can recognize the client and the client’s transactions.

Q15) What is the purpose of Object.defineProperties () method?

Object.defineProperties () method to create unique properties on a defined object. It provides various configuration events to initialize these members.

function Student (name) { this.name = name;
}
var student 1 = Object .create(Student tvp, properties ={
“subject”: {
value: “system”, writable: true, enumerable :true
},
“marks”: { value: 3, writable: false,
enumerable: true
}
Object. Define Properties (student1, properties); studenti.name = “Mani”:
student 1 .subject = “Mathematics”; student1 .marks=85;
console.log (student1);
Q16) Define the mechanism of the type of operator?

Type of operator, in C#, is an operator used to decide the type of the parameter passed to it. … The highlight of reflection in the .NET frame is a powerful device by which the skills of a type can be known and used at runtime.

Q17) What are the meanings of undefined variables and undeclared variables?

Undefined variables are the types of variables which gets said in the program. However, the value of undefined variables is not implemented in the JavaScript programming style. The value gets replaced if one tries to read the undefined value.

Q18) What is try catch in JavaScript?

JavaScript Errors – Throw and Try to Catch.The catch comment show handle the error. The throw statement lets you perform custom errors. The final report lets you execute code, after try and catch, blind of the result.

Q19) What is the role of JavaScript in a web page?

JavaScript, an object scripting program language which is used in web pages on with markup language HTML. JavaScript is quite successful and adopted largely by every web browser for its plan which provides dynamic content to get done in a webpage.

Q20) What is the ‘Strict’ mode in JavaScript and how can it be enabled?

Strict Mode adds certain needs to JavaScript. Under the strict mode, JavaScript gives errors for a piece of codes, which did not show and before the error, but might be uncertain and possibly unsafe. The strict mode also explains some mistakes that hamper the JavaScript engines to work efficiently.

Function my function ()

 { “Use strict”;
Var v = “This is a strict mode function”;
}
Q21) Why use JavaScript strict mode?
  • It catches some basic coding bloopers, delivering exceptions.
  • It prevents or throws errors when approximately “unsafe” actions are taken (such as getting access to the global object).
  • It disables comments that are difficult or poorly thought out.
Q22) 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.

Q23) What is the use of Push method in JavaScript?

The push method adds values to an array. push is purposely generic. This method can be used by a call() or apply() on objects following arrays. The push method relies on a space property to decide where to start embedding the assigned values

Q24) What does Pop () method of the array do?

The pop() method extracts the last element of an array and replaces that element. Note: This method modifies the length of an array. Tip: To remove the first portion of an array, use the shift() method.

Q25) What is unshift method in JavaScript?

Unshift() Method. The unshift() system is like the push() method, only it runs at the possibility of the array. The unshift() system can prepend one or more components to the opening of an array. This changes the display on which the program was called.

Q26) What does .push do in JavaScript?

The push() method is added to new items end of an array and returns the new length. The new item(s) will be attached at the end of the design. To add items at the start of an array, use the unshift() method.

Q27) What is object in Javascript?

JavaScript is designed on a simple object-based paradigm. An object is a set of features, and a property is an organization within a name (or key) and a value. A property’s value container is a function, in which case the field is recognized as a method.

Q28) Is Exception handling possible in Javascript?

When a JavaScript statement makes an error, it is said to throw an exception. Instead of moving to this next statement, the JavaScript decoder checks for exception handling code. If there is any no exception handler, then the program passes throughway from whatever function started the exception.

Q29) How do I fix JavaScript errors?

Open the Console. Go to the cover where you are encountering the error. In Chrome, operate to View > Developer > JavaScript Console or Extra Tools > JavaScript Console or press Ctrl + Shift + J. Recognize the Error. The error console will open. If you don’t notice all errors try reloading the web page.

Q30) What is error handling in JavaScript?

JavaScript Errors – Throw and Try to Catch. The try statement method lets you experiment a block of code for errors. The catch error statement lets you handle the error. The throw record lets you perform custom systemic errors.

Q31) What would be the output of following code ?

function mul(a) { return function(b) {
return function(c) { return function(e) {
return function(p) { return a * b * c * e * p;
};
};
};
};
}
console.log(mul(2)(3)(4)(5)(6));

1.480
2.Reference 3.Type 4.Undefined 1)480

Q32) What Is The Difference Between Sessionstate And Viewstate?

Session State persists the data of a special user in the server. This data available till user end the browser or session time effects. View State is valid essentially during postbacks and information is stored in the client side only. … Moreover, ViewState are not obtained as data is displayed to the client.

Q33) Can Javascript Code Be Broken In Different Lines?

Breaking is likely within a string statement by using a backslash at the end but no within any other javascript statement.
document.write(“Hello world”);
is possible but not document. write (“hello world”);

Q34) Is A Javascript Script Faster Than An Asp Script?

Yes. Since javascript is a client-side scripting it does need the web server’s help for its estimate, so it is always quicker than any server-side scripting like ASP, PHP,etc..

Q35) How are object properties assigned?

Properties in the destination object will be overwritten by properties within the sources if they have the same key. … The Object.assign() only copies enumerable and own properties from a beginning object to a target object.

Q36) What are the different types of errors in JavaScript?

Load time errors: Errors which come up when storing a web page like odd syntax errors are known as Load-time errors and it makes the errors dynamically.
Runtime errors: In this error come due to abuse of the command inside the HTML language.
Logical Errors: These are the errors that occur due to the poor logic performed on a function which is just a different operation.

Q37) What are non primitive data types in JavaScript?

Data types that are known as primitive data values in JavaScript are numbers, strings, booleans, null, undefined. Objects such as functions and arrays are pointed to as non-primitive values. The fundamental difference between primitives and non-primitives is that primitives are permanent and non-primitives are mutable.

Q38) Which keywords are used to handle exceptions?

It’s used to an own expectation. It is done when the application Program does not manage exception via try block.It manages explicitly thrown exceptions. It handles all exceptions made generate by the program.

Q39) What is the use of blur function?

The blur event occurs when a component loses focus. The blur() method triggers the blur event or adds a function to run when a blur effect occurs. This method is often used commonly with the focus() program.

Q40) Can JavaScript react to events?

Reacting to Events. A JavaScript can be done executed when an event occurs, like when a user to clicks on an HTML element. Examples of HTML events: When a user clicks to the mouse.

Q41) What is the function of delete operator?

Delete keywords using to deleted the property as well as value. Example :
var student= {age:18, batch:”abc”}; delete student. Age;

Q42) Methods Get And Post In Html Forms – What’s The Difference?

In HTML, one can define two different resignation means for a form. The method is defined inside a FORM element, using the METHOD property. The difference between METHOD=”GET” (the error) and METHOD=”POST” is originally defined in terms of form data encoding. Differences in form submission.

Q43) What Is A Hypertext Link?

A hypertext link is a unique tag that links one page to another page or resource. If you click the link, the browser takes to the link’s destination.

Q44) Explain how can you submit a form using JavaScript?

In the javascript onclick event function, you can using to form.submit() method to submit a form. You can perform submit work by application, submit button, by clicking on the hyperlink, button, and image tag etc. You can also execute javascript form submission by form connects like id, name, class, tag name as well.
To submit a form using JavaScript use document.form[0].submit();

Q45) Does JavaScript support automatic type conversion?

JavaScript is a “loosely typed” Programming language, which indicates that whenever an operator or statement is requiring a particular data-type, JavaScript will automatically change the data to that type.

Q46) How does return work in JavaScript?

In the JavaScript function, return statements terminate execution in a function and return a value to the caller; JavaScript functions require an explicit return receipt for returning the result of an appearance (the value) from each function. When a return value statement is not present, the interpreter automatically returns an undefined value.

Q47) how can the style/class of an element be changed?

To change the all classes for an element: To alter all absolute classes with one or added new classes, set the className attribute: document.getElementById(“MyElement”).className = “MyClass”;
Example : document.getElementById(“myText”).style.fontSize = “35?; or
document.getElementById(“myText”).className = “anystudent”;

Q48) What is the difference between JavaScript and JScript?

JScript is the Microsoft dialect language of the ECMAScript scripting programming language specification. Netscape and Mozilla implement to the Javascript ECMAScript JScript, and ECMAScript is very similar program coding languages. In fact, the name “JavaScript” usually refers to ECMAScript or JScript.

Q49) What is eval JavaScript?

Eval is a function of global object property.In this eval() argument function is a string. If the argument is one or more JavaScript comments, eval() executes the statements.

Q50) What is called Variable typing in Javascript?

Variable typing is used to select a number to a variable and the same variable can be assigned to a string Variable.
Example :
i = 20;
i = “string”;

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