Javascript Interview Questions For 5 Years Experience
Common Javascript Interview Questions for Candidates with 5 Years of Experience
Javascript is a widely used scripting language for creating dynamic and interactive web applications. As a language that evolves constantly, it is important for a candidate with 5 years of experience to be up-to-date with the latest developments and have a strong foundation in the language. During an interview, the candidate may be tested on various topics such as core concepts, data types, object-oriented programming, DOM manipulation, Ajax, and error handling. Additionally, they may be asked to solve real-world coding problems and demonstrate their debugging skills. Employers may also look for knowledge of JavaScript frameworks such as React, Angular, or Vue, and familiarity with browser compatibility issues. Strong problem-solving and communication skills are also important for a successful interview.
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1 - What is the difference between var, let, and const in JavaScript?
Var is used to declare variables in a global or local scope, while let and const are block scoped, meaning they can only be accessed within the block of code they are declared in.
Var can be redeclared and reassigned, while let can only be reassigned and const cannot be reassigned.
Variables declared with var are hoisted to the top of the code, while let and const are not hoisted.
Overall, const should be used for variables that will not be reassigned, let should be used for variables that will be reassigned, and var should be avoided due to its unpredictable behavior.
2) What is a closure in JavaScript and how does it work?
A closure is a function that has access to variables in its outer scope, even after the outer function has returned.
This is made possible by the fact that functions in JavaScript are first class citizens, meaning they can be passed around as objects.
When an inner function is returned from the outer function, the inner function will remember the variables in the scope of the outer function.
This can be useful for creating private variables and encapsulating code.
3) What are the different data types in JavaScript?
JavaScript has six primitive data types: string, number, boolean, null, undefined, and symbol.
It also has one complex data type: object, which includes arrays, functions, and objects.
Symbols were introduced in ES6 and are unique and immutable, while objects are mutable.
Null represents the intentional absence of a value, while undefined represents the absence of a defined value.
4) Explain the event loop in JavaScript.
The event loop is a mechanism in JavaScript that allows for asynchronous and non blocking code execution.
It continuously checks the call stack for any functions that need to be executed and if there are none, it checks the task queue for any pending tasks.
If there are tasks in the queue, they are pushed onto the call stack for execution.
This process ensures that JavaScript can handle multiple tasks at once, without blocking other code from running.
5) What is a promise in JavaScript?
A promise is a placeholder for a future value that will be returned asynchronously.
It has three states: pending, fulfilled, and rejected.
A promise is used to handle asynchronous operations and provides a cleaner way of writing asynchronous code compared to using callbacks.
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It allows for chaining of multiple asynchronous operations and handling of errors using the .catch() method.
6) What is the difference between == and === in JavaScript?
The triple equals (===) is a strict equality operator, meaning both value and type must be equal for the expression to return true.
The double equals (==) is a loose equality operator, meaning it only compares the values and will perform type coercion if necessary.
For example, 3 === ‘3’ will return false, but 3 == ‘3’ will return true since the value is the same and the string will be converted to a number during the comparison.
7) How do you handle errors in JavaScript?
Errors can be handled using the try…catch statement in JavaScript.
The code that may cause an error is enclosed in the try block, and if an error occurs, it is caught in the catch block.
The catch block can also take an optional parameter, which is the error object, allowing for more specific error handling.
The finally block can also be used to execute code regardless of whether an error was caught or not.
8) What is the difference between let and var in JavaScript?
Let is block scoped, meaning it can only be accessed within the block of code it is declared in, while var is function scoped and can be accessed within the entire function.
Variables declared with var are hoisted to the top of the function or global scope, while let is not hoisted and will throw an error if accessed before being declared.
Var can be redeclared and reassigned, while let can only be reassigned.
9) What is the difference between a shallow copy and deep copy in JavaScript?
A shallow copy creates a new object and references the same values as the original object.
This means that changes made to the original object will also be reflected in the shallow copy.
A deep copy creates a new object and copies the values from the original object, creating a separate, independent object.
This means that changes made to the original object will not affect the deep copy.
Shallow copies can be achieved using Object.assign() or the spread operator, while deep copies require cloning functions or libraries.
10) What are the different ways to declare a variable in JavaScript?
Variables can be declared using the var, let, and const keywords.
They can also be declared without any keyword, which will make the variable a global variable if it is declared outside a function, or a local variable if it is declared inside a function.
Variable names must start with a letter, underscore, or dollar sign, and can contain letters, numbers, underscores, or dollar signs.
11) How does JavaScript handle memory management?
JavaScript uses a garbage collector to automatically manage memory.
This means that developers do not need to manually allocate or deallocate memory for variables.
However, this also means that developers must be mindful of creating memory leaks by holding onto references to objects that are no longer needed.
12) What is the scope chain in JavaScript?
The scope chain is the hierarchy of variables in nested scopes in JavaScript.
When a variable is accessed, JavaScript will start with the innermost scope and work its way up the chain until it finds a variable with the same name.
This is also known as lexical scoping.
13) How do you host a website written in JavaScript?
A website written in JavaScript can be hosted on a web server.
This can be a physical server or a cloud based server.
The files of the website can be uploaded to the server using an FTP client or through the web host's control panel.
Some hosting services also provide pre configured environments for hosting JavaScript websites.
14) What is the difference between null and undefined in JavaScript?
Null represents the intentional absence of a value, while undefined represents a variable that has been declared but not assigned a value.
Variables that have not been declared, or properties that do not exist, will have a value of undefined.
Null is often set as a value by developers, while undefined is a default value set by the JavaScript engine.
15) How do you handle asynchronous operations in JavaScript?
Asynchronous operations can be handled using callbacks, promises, or Async/Await.
Callbacks are functions passed as arguments to the asynchronous operation and executed once the operation is complete.
Promises use the .then() and .catch() methods to handle the outcome of an asynchronous operation.
Async/Await is a newer syntax introduced in ES8, which allows for writing asynchronous code in a synchronous style.
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