How Do You Redeclare Variables In Switch Block Without An Error
If you try to redeclare variables in a switch block then it will cause errors because there is only one block. For example, the below code block throws a syntax error as below,
letcounter=1 switch
To avoid this error, you can create a nested block inside a case clause and create a new block scoped lexical environment.
letcounter=1 switchcase1: }
Essential Javascript Interview Questions
What is the method for reading and writing a file in JavaScript?What is the purpose of this operator in JavaScript?What is the role of break and continue statements?What is the use of blur function?What is the use of isNaN function?What is the use of Push method in JavaScript?What is the use of type of operator?What is the use of Void?What is the way to get the status of a CheckBox?What is unshift method in JavaScript?What is variable typing?What typeof returns for a null value?Whether JavaScript has concept level scope?Which built-in method adds one or more elements to the end of an array and returns the new length of the array?Which built-in method calls a function for each element in the array?Which built-in method combines the text of two strings and returns a new string?Which built-in method removes the last element from an array and returns that element?Which built-in method returns the calling string value converted to lower case?Which built-in method returns the calling string value converted to upper case?Which built-in method returns the character at the specified index?Which built-in method returns the characters in a string beginning at the specified location?Which built-in method returns the index within the calling String object of the first occurrence of the specified value?Which built-in method returns the length of the string?Which built-in method returns the string representation of the numbers value?
What Are Generator Functions
Introduced in the ES6 version, generator functions are a special class of functions.They can be stopped midway and then continue from where they had stopped.Generator functions are declared with the function* keyword instead of the normal function keyword:
function* genFunc
In normal functions, we use the return keyword to return a value and as soon as the return statement gets executed, the function execution stops:
functionnormalFunc
In the case of generator functions, when called, they do not execute the code, instead, they return a generator object. This generator object handles the execution.
function* genFuncgenFunc // Returns Object
The generator object consists of a method called next, this method when called, executes the code until the nearest yield statement, and returns the yield value.For example, if we run the next method on the above code:
genFunc.next // Returns
As one can see the next method returns an object consisting of a value and done properties. Value property represents the yielded value. Done property tells us whether the function code is finished or not. .
Generator functions are used to return iterators. Lets see an example where an iterator is returned:
function* iteratorFunc return count }let iterator = iteratorFunc console.log) // console.log) // console.log) //
As you can see in the code above, the last line returns done:true, since the code reaches the return statement.
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What Are Some Important Javascript Unit Testing Frameworks
Following is a curated list of popular JavaScript Unit Testing Frameworks and Tools that are widely used :
Unit.js: It is known as an open-source assertion library running on browser and Node.js. It is extremely compatible with other JavaScript Unit Testing frameworks like Mocha, Karma, Jasmine, QUnit, Protractor, etc. Provides the full documented API of assertion list.
QUnit: It is used for both client-side and server-side JavaScript Unit Testing. This Free JavaScript testing framework is used for jQuery projects. It follows Common JS unit testing Specification for unit testing in JavaScript. It supports the Node Long-term Support Schedule.
Jasmine: Jasmine is the behavior-driven development framework to unit test JavaScript. It is used for testing both synchronous and asynchronous JavaScript codes. It does not require DOM and comes with an easy syntax that can be written for any test.
Karma: Karma is an open-source productive testing environment. Easy workflow control running on the command line. Offers the freedom to write the tests with Jasmine, Mocha, and QUnit. You can run the test on real devices with easy debugging.
Mocha: Mocha runs on Node.js and in the browser. Mocha performs asynchronous testing more simply. Provides accuracy and flexibility in reporting. Provides tremendous support of rich features such as test-specific timeouts, JavaScript APIs.
What Is A Decorator
A decorator is an expression that evaluates to a function and that takes the target, name, and decorator descriptor as arguments. Also, it optionally returns a decorator descriptor to install on the target object. Let’s define admin decorator for user class at design time,
functionadmin}@adminclassUserconsole.log //true @adminclassUserconsole.log //false
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What Are Undeclared And Undefined Variables
Undeclared variables are those that do not exist in a program and are not declared. If the program tries to read the value of an undeclared variable, then a runtime error is encountered.
Undefined variables are those that are declared in the program but have not been given any value. If the program tries to read the value of an undefined variable, an undefined value is returned.
What Is The Purpose Of The Let Keyword
The let statement declares a block scope local variable. Hence the variables defined with let keyword are limited in scope to the block, statement, or expression on which it is used. Whereas variables declared with the var keyword used to define a variable globally, or locally to an entire function regardless of block scope.
Let’s take an example to demonstrate the usage,
letcounter=30 ifconsole.log // 30
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What Is The Use Of Preventdefault Method
The preventDefault method cancels the event if it is cancelable, meaning that the default action or behaviour that belongs to the event will not occur. For example, prevent form submission when clicking on submit button and prevent opening the page URL when clicking on hyperlink are some common use cases.
document.getElementById.addEventListener)
Note: Remember that not all events are cancelable.
How Is Collection Different From Collections In Java
Collection is an interface whereas Collections is a java utility class containing only static methods that can operate on collections like ArrayList, Set, Queue, etc. and both belong to Collection Framework and are present in the java.util package.
Since Collection is an interface dealing with the data type of iterable objects, the interface extends the Iterable interface as shown below:
publicinterfaceCollection< E> extendsIterable< E>
Since Collections is a java class, it extends the Object class as shown below:
publicclassCollectionsextendsObject
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Faqs On Java Interview Questions For Professionals With 5 Years Of Experience
Q1. What is the salary of a Java Developer with 5 years of experience?The average salary of a Java Developer with 5 years of work experience is approximately $100,682 per year.
Q2. What is the future of experienced Java Developer jobs?
Based on surveys conducted by Stackoverflow and Dice, experienced Java developers are still in popular demand and have a higher pay compared to other programming languages. Even though new programming languages are continuously coming up, Java has continually evolved to catch up with them. Besides, many tech giants rely on Java to run their systems and continue to do so for many years since completely refactoring them all at once is not feasible.
Q3. Which companies use Java?A. Some of the major companies that use Java to run their systems are Google, Netflix, Instagram, Uber, Spotify, Airbnb, Pinterest, Netflix, Amazon, Slack, and many more.
Q4. What are the top skills an experienced Java Developer should have?A. Besides basic Java skills, the top advanced skills an experienced Java Developer should work on are â AI and machine learning, Python, Blockchain, Amazon Web Services, Mobile technologies such as Android and OS, Hadoop/Big Data, Advanced JavaScript framework such as Angular, React, and VueJS, and Spring Boot/microservices.
Q5. What are the top Java interview questions for 5 years of experienced developers?
What Is The Purpose Of Error Object
The Error constructor creates an error object and the instances of error objects are thrown when runtime errors occur. The Error object can also be used as a base object for user-defined exceptions. The syntax of error object would be as below,
newError
You can throw user defined exceptions or errors using Error object in try…catch block as below,
trycatch
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Is There Any Difference In Defining Or Creating A String By Using String Literal And By Using The New Operator
Creating string using the new operator ensures that the String is created in the heap alone and not into the string pool. Whereas, creating string using literal ensures that the string is created in the string pool. String pool exists as part of the perm area in the heap. This ensures that the multiple Strings created using literal having same values are pointed to one object and prevents duplicate objects with the same value from being created.
What Is The Working Of Timers In Javascript
Timers are used to execute a piece of code at a set time or repeat the code in a given interval. This is done by using the functions setTimeout, setInterval, and clearInterval.
The setTimeout function is used to start a timer that calls a particular function after the mentioned delay. The setInterval function repeatedly executes the given function in the mentioned delay and only halts when canceled. The clearInterval function instructs the timer to stop.
Timers are operated within a single thread, and thus events might queue up, waiting to be executed.
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What Is The Purpose Of Evalerror Object
The EvalError object indicates an error regarding the global eval function. Even though this exception is not thrown by JavaScript anymore, the EvalError object remains for compatibility. The syntax of this expression would be as below,
newEvalError
You can throw EvalError with in try…catch block as below,
trycatch{console.log // "Eval function error", "EvalError", "someFile.js"
How Do You Empty A Javascript Array
Arrays are widely used in JavaScript, making understanding their behavior and possible operations crucial when working with JavaScript. An interviewer might ask a JS question like this to gauge the candidates familiarity with JavaScript arrays and their operators. You, as the candidate should be ready to explain a couple of different approaches and how they work at a high level.
There are various ways to empty an array in JavaScript. Below are a few common ways to do it.
targetArray =
targetArray.length = 0
targetArray.splice
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How Do You Reuse Information Across Service Worker Restarts
The problem with service worker is that it gets terminated when not in use, and restarted when it’s next needed, so you cannot rely on global state within a service worker’s onfetch and onmessage handlers. In this case, service workers will have access to IndexedDB API in order to persist and reuse across restarts.
What Is A Comma Operator
The comma operator is used to evaluate each of its operands from left to right and returns the value of the last operand. This is totally different from comma usage within arrays, objects, and function arguments and parameters. For example, the usage for numeric expressions would be as below,
varx=1 x= console.log // 2
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Is Javascript A Pass
The variable’s data is always a reference for objects, hence it’s always pass by value. As a result, if you supply an object and alter its members inside the method, the changes continue outside of it. It appears to be pass by reference in this case. However, if you modify the values of the object variable, the change will not last, demonstrating that it is indeed passed by value.
What Do You Understand By Event Bubbling
Ans: Event flow specifies the order in which events are received on the page from the element where the event occurs and propagated through the DOM tree. There are two main event models: event bubbling and event capturing.
In the event bubbling model , an event starts at the most particular element and then flows upward toward the least specific element i.e., the document or even the window. For example, you have a div element and a button inside the div element when the button triggers a click event, the click event occurs in the following order:
The click event first occurs on the button, which is the element that was clicked. Then the click event goes up the DOM tree, firing on each node along its way until it reaches the document object. Few web browsers these days will bubble the event up to the window object.
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Java Thread Interview Questions For Developers With 5 Years Experience
When preparing for your Java Advanced interview, you should also practice some Java Thread interview questions and answers for 5 years of experienced professionals. Here are some sample Java Thread interview questions:
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Leave no stone unturned for your Java interview preparation. Study every aspect of a Java interview for developers with 5 years of experience. Be thorough about programming data structures and algorithms, systems design, and specific domain know-how about JavaScript, along with in-depth preparation for behavioral and leadership interview rounds. Experts recommend practicing mock interviews and Java interview questions before you face the actual interview to boost your confidence and prepare you for all kinds of interview situations.
At Interview Kickstart, you can practice mock interviews with experts and hiring managers from FAANG companies. Their valuable feedback has gone a long way in helping Java professionals such as yourself crack tech interviews at the top FAANG companies.
Javascript Interview Questions For 2 Years Experienced
It is basically an object-oriented programming language that is having a lot of applications. It can be used for both server-side, as well as client-side scripting and the good thing is it is known to provide the best results in every aspect. When it comes to building HTML WebPages, this language is often considered and is known to bring the most desired outcomes.
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Explain Implicit Type Coercion In Javascript
Automatic value conversion from one data type to another data type is known as Implicit type coercion in JavaScript. There are many types Number to String, String to Number, Boolean to Number etc. When different values are applied to the datatypes that are not of that value it automatically converts them.
The time when the number is added to a string, it converts the number type as a string type with the help of the + operator.
Example:
var a = 4
var b = 5 //number thats inside double quotes indicate its been considered as a string
a + b // Returns 45
var q = Hi // Here the number 45 is been concatenated with the string
p + q // Returns 45Hi
NOTE: We can use the operator as well, but the number which we give will be converted to string datatype and subtracted
Example:
var p = 5
var q = 5
p q //Returns 0 since the variable q is converted to a number type
When we use logical operators, if statements, ternary operators and loop checks Boolean coercion takes place. We have to ensure properly the truthy and falsy values.
Except 0, O, -0, , Null, undefined and Nan all others are truthy values
Example:
var b = 24 // variable declaration with value
if // Since the a value is 0 the code will not run
if // Since the b value is 24 the code will run
OR operator The first value is returned only when it is truthy else the second value gets returned.
| Operator |
| Second Value |
Example:
Equality Coercion
Give An Example Where Do You Really Need Semicolon
It is recommended to use semicolons after every statement in JavaScript. For example, in the below case it throws an error “.. is not a function” at runtime due to missing semicolon.
// define a functionvarfn=))
and it will be interpreted as
varfn=))
In this case, we are passing the second function as an argument to the first function and then trying to call the result of the first function call as a function. Hence, the second function will fail with a “… is not a function” error at runtime.
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What Is The Difference Between An Attribute And A Property
Attributes are defined on the HTML markup whereas properties are defined on the DOM. For example, the below HTML element has 2 attributes type and value,
< inputtype="text"value="Name:">
You can retrieve the attribute value as below,
constinput=document.querySelector console.log) // Good morningconsole.log // Good morning
And after you change the value of the text field to “Good evening”, it becomes like
console.log) // Good eveningconsole.log // Good evening
What Is The Purpose Of Double Exclamation
The double exclamation or negation ensures the resulting type is a boolean. If it was falsey , it will be false, otherwise, true.For example, you can test IE version using this expression as below,
letisIE8=false isIE8=!!navigator.userAgent.match console.log // returns true or false
If you don’t use this expression then it returns the original value.
console.log) // returns either an Array or null
Note: The expression !! is not an operator, but it is just twice of ! operator.
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