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JavaScript Top 500 Interview Questions
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| Questions |
| What are the possible ways to create objects in JavaScript |
| What is prototype chain |
| What is the difference between Call, Apply and Bind |
| What is JSON and its common operations |
| What is the purpose of the array slice method |
| What is the purpose of the array splice method |
| What is the difference between slice and splice |
| How do you compare Object and Map |
| What is the difference between == and === operators |
| What are lambda or arrow functions |
| What is a first class function |
| What is a first order function |
| What is a higher order function |
| What is a unary function |
| What is the currying function |
| What is a pure function |
| What is the purpose of the let keyword |
| What is the difference between let and var |
| What is the reason to choose the name let as a keyword |
| How do you redeclare variables in switch block without an error |
| What is the Temporal Dead Zone |
| What is IIFE(Immediately Invoked Function Expression) |
| How do you decode or encode a URL in JavaScript? |
| What is memoization |
| What is Hoisting |
| What are classes in ES6 |
| What are closures |
| What are modules |
| Why do you need modules |
| What is scope in javascript |
| What is a service worker |
| How do you manipulate DOM using a service worker |
| How do you reuse information across service worker restarts |
| What is IndexedDB |
| What is web storage |
| What is a post message |
| What is a cookie |
| Why do you need a Cookie |
| What are the options in a cookie |
| How do you delete a cookie |
| What are the differences between cookie, local storage and session storage |
| What is the main difference between localStorage and sessionStorage |
| How do you access web storage |
| What are the methods available on session storage |
| What is a storage event and its event handler |
| Why do you need web storage |
| How do you check web storage browser support |
| How do you check web workers browser support |
| Give an example of web worker |
| What are the restrictions of web workers on DOM |
| What is a promise |
| Why do you need a promise |
| What are the three states of promise |
| What is a callback function |
| Why do we need callbacks |
| What is a callback hell |
| What is server-sent events |
| How do you receive server-sent event notifications |
| How do you check browser support for server-sent events |
| What are the events available for server sent events |
| What are the main rules of promise |
| What is callback in callback |
| What is promise chaining |
| What is promise.all |
| What is the purpose of race method in promise |
| What is a strict mode in javascript |
| Why do you need strict mode |
| How do you declare strict mode |
| What is the purpose of double exclamation |
| What is the purpose of delete operator |
| What is typeof operator |
| What is undefined property |
| What is null value |
| What is the difference between null and undefined |
| What is eval |
| What is the difference between window and document |
| How do you access history in javascript |
| How do you detect caps lock key turned on or not |
| What is isNaN |
| What are the differences between undeclared and undefined variables |
| What are global variables |
| What are the problems with global variables |
| What is NaN property |
| What is the purpose of isFinite function |
| What is an event flow |
| What is event bubbling |
| What is event capturing |
| How do you submit a form using JavaScript |
| How do you find operating system details |
| What is the difference between document load and DOMContentLoaded events |
| What is the difference between native, host and user objects |
| What are the tools or techniques used for debugging JavaScript code |
| What are the pros and cons of promises over callbacks |
| What is the difference between an attribute and a property |
| What is same-origin policy |
| What is the purpose of void 0 |
| Is JavaScript a compiled or interpreted language |
| Is JavaScript a case-sensitive language |
| Is there any relation between Java and JavaScript |
| What are events |
| Who created javascript |
| What is the use of preventDefault method |
| What is the use of stopPropagation method |
| What are the steps involved in return false |
| What is BOM |
| What is the use of setTimeout |
| What is the use of setInterval |
| Why is JavaScript treated as Single threaded |
| What is an event delegation |
| What is ECMAScript |
| What is JSON |
| What are the syntax rules of JSON |
| What is the purpose JSON stringify |
| How do you parse JSON string |
| Why do you need JSON |
| What are PWAs |
| What is the purpose of clearTimeout method |
| What is the purpose of clearInterval method |
| How do you redirect new page in javascript |
| How do you check whether a string contains a substring |
| How do you validate an email in javascript |
| How do you get the current url with javascript |
| What are the various url properties of location object |
| How do get query string values in javascript |
| How do you check if a key exists in an object |
| How do you loop through or enumerate javascript object |
| How do you test for an empty object |
| What is an arguments object |
| How do you make first letter of the string in an uppercase |
| What are the pros and cons of for loop |
| How do you display the current date in javascript |
| How do you compare two date objects |
| How do you check if a string starts with another string |
| How do you trim a string in javascript |
| How do you add a key value pair in javascript |
| Is the '!--' notation represents a special operator |
| How do you assign default values to variables |
| How do you define multiline strings |
| What is an app shell model |
| Can we define properties for functions |
| What is the way to find the number of parameters expected by a function |
| What is a polyfill |
| What are break and continue statements |
| What are js labels |
| What are the benefits of keeping declarations at the top |
| What are the benefits of initializing variables |
| What are the recommendations to create new object |
| How do you define JSON arrays |
| How do you generate random integers |
| Can you write a random integers function to print integers with in a range |
| What is tree shaking |
| What is the need of tree shaking |
| Is it recommended to use eval |
| What is a Regular Expression |
| What are the string methods available in Regular expression |
| What are modifiers in regular expression |
| What are regular expression patterns |
| What is a RegExp object |
| How do you search a string for a pattern |
| What is the purpose of exec method |
| How do you change style of a HTML element |
| What would be the result of 1+2+'3' |
| What is a debugger statement |
| What is the purpose of breakpoints in debugging |
| Can I use reserved words as identifiers |
| How do you detect a mobile browser |
| How do you detect a mobile browser without regexp |
| How do you get the image width and height using JS |
| How do you make synchronous HTTP request |
| How do you make asynchronous HTTP request |
| How do you convert date to another timezone in javascript |
| What are the properties used to get size of window |
| What is a conditional operator in javascript |
| Can you apply chaining on conditional operator |
| What are the ways to execute javascript after page load |
| What is the difference between proto and prototype |
| Give an example where do you really need semicolon |
| What is a freeze method |
| What is the purpose of freeze method |
| Why do I need to use freeze method |
| How do you detect a browser language preference |
| How to convert string to title case with javascript |
| How do you detect javascript disabled in the page |
| What are various operators supported by javascript |
| What is a rest parameter |
| What happens if you do not use rest parameter as a last argument |
| What are the bitwise operators available in javascript |
| What is a spread operator |
| How do you determine whether object is frozen or not |
| How do you determine two values same or not using object |
| What is the purpose of using object is method |
| How do you copy properties from one object to other |
| What are the applications of assign method |
| What is a proxy object |
| What is the purpose of seal method |
| What are the applications of seal method |
| What are the differences between freeze and seal methods |
| How do you determine if an object is sealed or not |
| How do you get enumerable key and value pairs |
| What is the main difference between Object.values and Object.entries method |
| How can you get the list of keys of any object |
| How do you create an object with prototype |
| What is a WeakSet |
| What are the differences between WeakSet and Set |
| List down the collection of methods available on WeakSet |
| What is a WeakMap |
| What are the differences between WeakMap and Map |
| List down the collection of methods available on WeakMap |
| What is the purpose of uneval |
| How do you encode an URL |
| How do you decode an URL |
| How do you print the contents of web page |
| What is the difference between uneval and eval |
| What is an anonymous function |
| What is the precedence order between local and global variables |
| What are javascript accessors |
| How do you define property on Object constructor |
| What is the difference between get and defineProperty |
| What are the advantages of Getters and Setters |
| Can I add getters and setters using defineProperty method |
| What is the purpose of switch-case |
| What are the conventions to be followed for the usage of swtich case |
| What are primitive data types |
| What are the different ways to access object properties |
| What are the function parameter rules |
| What is an error object |
| When you get a syntax error |
| What are the different error names from error object |
| What are the various statements in error handling |
| What are the two types of loops in javascript |
| What is nodejs |
| What is an Intl object |
| How do you perform language specific date and time formatting |
| What is an Iterator |
| How does synchronous iteration works |
| What is an event loop |
| What is call stack |
| What is an event queue |
| What is a decorator |
| What are the properties of Intl object |
| What is an Unary operator |
| How do you sort elements in an array |
| What is the purpose of compareFunction while sorting arrays |
| How do you reversing an array |
| How do you find min and max value in an array |
| How do you find min and max values without Math functions |
| What is an empty statement and purpose of it |
| How do you get meta data of a module |
| What is a comma operator |
| What is the advantage of a comma operator |
| What is typescript |
| What are the differences between javascript and typescript |
| What are the advantages of typescript over javascript |
| What is an object initializer |
| What is a constructor method |
| What happens if you write constructor more than once in a class |
| How do you call the constructor of a parent class |
| How do you get the prototype of an object |
| What happens If I pass string type for getPrototype method |
| How do you set prototype of one object to another |
| How do you check whether an object can be extendable or not |
| How do you prevent an object to extend |
| What are the different ways to make an object non-extensible |
| How do you define multiple properties on an object |
| What is MEAN in javascript |
| What Is Obfuscation in javascript |
| Why do you need Obfuscation |
| What is Minification |
| What are the advantages of minification |
| What are the differences between Obfuscation and Encryption |
| What are the common tools used for minification |
| How do you perform form validation using javascript |
| How do you perform form validation without javascript |
| What are the DOM methods available for constraint validation |
| What are the available constraint validation DOM properties |
| What are the list of validity properties |
| Give an example usage of rangeOverflow property |
| Is enums feature available in javascript |
| What is an enum |
| How do you list all properties of an object |
| How do you get property descriptors of an object |
| What are the attributes provided by a property descriptor |
| How do you extend classes |
| How do I modify the url without reloading the page |
| How do you check whether an array includes a particular value or not |
| How do you compare scalar arrays |
| How to get the value from get parameters |
| How do you print numbers with commas as thousand separators |
| What is the difference between java and javascript |
| Does javascript supports namespace |
| How do you declare namespace |
| How do you invoke javascript code in an iframe from parent page |
| How do get the timezone offset from date |
| How do you load CSS and JS files dynamically |
| What are the different methods to find HTML elements in DOM |
| What is jQuery |
| What is V8 JavaScript engine |
| Why do we call javascript as dynamic language |
| What is a void operator |
| How to set the cursor to wait |
| How do you create an infinite loop |
| Why do you need to avoid with statement |
| What is the output of below for loops |
| List down some of the features of ES6 |
| What is ES6 |
| Can I redeclare let and const variables |
| Is const variable makes the value immutable |
| What are default parameters |
| What are template literals |
| How do you write multi-line strings in template literals |
| What are nesting templates |
| What are tagged templates |
| What are raw strings |
| What is destructuring assignment |
| What are default values in destructuring assignment |
| How do you swap variables in destructuring assignment |
| What are enhanced object literals |
| What are dynamic imports |
| What are the use cases for dynamic imports |
| What are typed arrays |
| What are the advantages of module loaders |
| What is collation |
| What is for...of statement |
| What is the output of below spread operator array |
| Is PostMessage secure |
| What are the problems with postmessage target origin as wildcard |
| How do you avoid receiving postMessages from attackers |
| Can I avoid using postMessages completely |
| Is postMessages synchronous |
| What paradigm is Javascript |
| What is the difference between internal and external javascript |
| Is JavaScript faster than server side script |
| How do you get the status of a checkbox |
| What is the purpose of double tilde operator |
| How do you convert character to ASCII code |
| What is ArrayBuffer |
| What is the output of below string expression |
| What is the purpose of Error object |
| What is the purpose of EvalError object |
| What are the list of cases error thrown from non-strict mode to strict mode |
| Do all objects have prototypes |
| What is the difference between a parameter and an argument |
| What is the purpose of some method in arrays |
| How do you combine two or more arrays |
| What is the difference between Shallow and Deep copy |
| How do you create specific number of copies of a string |
| How do you return all matching strings against a regular expression |
| How do you trim a string at the beginning or ending |
| What is the output of below console statement with unary operator |
| Does javascript uses mixins |
| What is a thunk function |
| What are asynchronous thunks |
| What is the output of below function calls |
| How to remove all line breaks from a string |
| What is the difference between reflow and repaint |
| What happens with negating an array |
| What happens if we add two arrays |
| What is the output of prepend additive operator on falsy values |
| How do you create self string using special characters |
| How do you remove falsy values from an array |
| How do you get unique values of an array |
| What is destructuring aliases |
| How do you map the array values without using map method |
| How do you empty an array |
| How do you rounding numbers to certain decimals |
| What is the easiest way to convert an array to an object |
| How do you create an array with some data |
| What are the placeholders from console object |
| Is it possible to add CSS to console messages |
| What is the purpose of dir method of console object |
| Is it possible to debug HTML elements in console |
| How do you display data in a tabular format using console object |
| How do you verify that an argument is a Number or not |
| How do you create copy to clipboard button |
| What is the shortcut to get timestamp |
| How do you flattening multi dimensional arrays |
| What is the easiest multi condition checking |
| How do you capture browser back button |
| How do you disable right click in the web page |
| What are wrapper objects |
| What is AJAX |
| What are the different ways to deal with Asynchronous Code |
| How to cancel a fetch request |
| What is web speech API |
| What is minimum timeout throttling |
| How do you implement zero timeout in modern browsers |
| What are tasks in event loop |
| What are microtasks |
| What are different event loops |
| What is the purpose of queueMicrotask |
| How do you use javascript libraries in typescript file |
| What are the differences between promises and observables |
| What is heap |
| What is an event table |
| What is a microTask queue |
| What is the difference between shim and polyfill |
| How do you detect primitive or non primitive value type |
| What is babel |
| Is Node.js completely single threaded |
| What are the common use cases of observables |
| What is RxJS |
| What is the difference between Function constructor and function declaration |
| What is a Short circuit condition |
| What is the easiest way to resize an array |
| What is an observable |
| What is the difference between function and class declarations |
| What is an async function |
| How do you prevent promises swallowing errors |
| What is deno |
| How do you make an object iterable in javascript |
| What is a Proper Tail Call |
| How do you check an object is a promise or not |
| How to detect if a function is called as constructor |
| What are the differences between arguments object and rest parameter |
| What are the differences between spread operator and rest parameter |
| What are the different kinds of generators |
| What are the built-in iterables |
| What are the differences between for...of and for...in statements |
| How do you define instance and non-instance properties |
| What is the difference between isNaN and Number.isNaN? |
| How to invoke an IIFE without any extra brackets? |
| Is that possible to use expressions in switch cases? |
| What is the easiest way to ignore promise errors? |
| How do style the console output using CSS? |
| What is nullish coalescing operator(??)? |
| How do you group and nest console output? |
| What is the difference between dense and sparse arrays? |
| What are the different ways to create sparse arrays? |
| What is the difference between setTimeout, setImmediate and process.nextTick? |