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JavaScript Quiz Interview Questions
Q&A Quiz-style JavaScript Interview Questions
Covers critical topics
Answers by ex-interviewers
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Number of questions
195 questions
Total time
17 hours total
Questions List
Front End Quiz Interview Questions
Quiz-style front end interview questions — What to expect, concepts to learn, and 100+ important practice questions.
Guide
GUIDES
What is the difference between `==` and `===` in JavaScript?
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Difficulty
Easy
Topics
JavaScript
Users completed
3.44k done
What's the difference between a JavaScript variable that is: `null`, `undefined` or undeclared?
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Difficulty
Easy
Topics
JavaScript
Users completed
2.97k done
What's the difference between `.call` and `.apply` in JavaScript?
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Easy
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JavaScript
Users completed
2.7k done
What is the difference between `mouseenter` and `mouseover` event in JavaScript and browsers?
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Easy
Topics
Web APIs
HTML
JavaScript
Users completed
256 done
What are the various data types in JavaScript?
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Easy
Topics
JavaScript
Users completed
294 done
What is the difference between a `Map` object and a plain object in JavaScript?
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Easy
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JavaScript
Users completed
513 done
What are proxies in JavaScript used for?
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Easy
Topics
JavaScript
Users completed
131 done
Explain the concept of a callback function in asynchronous operations
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Difficulty
Easy
Topics
Async
JavaScript
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218 done
Explain the concept of a microtask queue
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Difficulty
Easy
Topics
Async
JavaScript
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182 done
Explain the concept of caching and how it can be used to improve performance
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Difficulty
Easy
Topics
JavaScript
Performance
Users completed
199 done
Explain the concept of code coverage and how it can be used to assess test quality
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Difficulty
Easy
Topics
JavaScript
Testing
Users completed
165 done
Explain the concept of Content Security Policy (CSP) and how it enhances security
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Difficulty
Easy
Topics
JavaScript
Security
Users completed
159 done
Explain the concept of Cross-Site Request Forgery (CSRF) and its mitigation techniques
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Difficulty
Easy
Topics
JavaScript
Networking
Security
Users completed
165 done
Explain the concept of debouncing and throttling
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Difficulty
Easy
Topics
Async
JavaScript
Performance
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193 done
Explain the concept of destructuring assignment for objects and arrays
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Easy
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JavaScript
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153 done
Explain the concept of error propagation in JavaScript
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Difficulty
Easy
Topics
JavaScript
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137 done
Explain the concept of hoisting with regards to functions
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Easy
Topics
JavaScript
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151 done
Explain the concept of inheritance in ES2015 classes
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Difficulty
Easy
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JavaScript
OOP
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125 done
Explain the concept of input validation and its importance in security
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Easy
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JavaScript
Security
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145 done
Explain the concept of lazy loading and how it can improve performance
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Easy
Topics
JavaScript
Performance
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170 done
Explain the concept of lexical scoping
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Easy
Topics
JavaScript
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142 done
Explain the concept of partial application
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Easy
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Closure
JavaScript
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121 done
Explain the concept of scope in JavaScript
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Easy
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JavaScript
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138 done
Explain the concept of tagged templates
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Easy
Topics
JavaScript
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96 done
Explain the concept of test-driven development (TDD)
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Easy
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JavaScript
Testing
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131 done
Explain the concept of the Prototype pattern
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Easy
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JavaScript
OOP
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111 done
Explain the concept of the Singleton pattern
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Easy
Topics
JavaScript
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107 done
Explain the concept of the spread operator and its uses
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Easy
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JavaScript
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131 done
Explain the concept of the Strategy pattern
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Easy
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JavaScript
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92 done
Explain the concept of the Web Socket API
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Easy
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JavaScript
Networking
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127 done
Explain the concept of `this` binding in event handlers
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Easy
Topics
Closure
Web APIs
JavaScript
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120 done
Explain the concept of tree shaking in module bundling
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Difficulty
Easy
Topics
JavaScript
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116 done
Explain the difference between classical inheritance and prototypal inheritance
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Easy
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JavaScript
OOP
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107 done
Explain the difference between `document.querySelector()` and `document.getElementById()`
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Difficulty
Easy
Topics
Web APIs
JavaScript
HTML
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163 done
Explain the difference between dot notation and bracket notation for accessing object properties
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Difficulty
Easy
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JavaScript
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119 done
Explain the difference between global scope, function scope, and block scope
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Easy
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JavaScript
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128 done
Explain the difference between shallow copy and deep copy
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Easy
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JavaScript
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117 done
Explain the difference between unit testing, integration testing, and end-to-end testing
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Easy
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JavaScript
Testing
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117 done
Explain the difference in hoisting between `var`, `let`, and `const`
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Difficulty
Easy
Topics
JavaScript
Users completed
133 done
Explain the different states of a Promise
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Difficulty
Easy
Topics
Async
JavaScript
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151 done
Explain the different ways the `this` keyword can be bound
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Easy
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Closure
JavaScript
Users completed
118 done
Explain the event phases in a browser
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Easy
Topics
Browser
JavaScript
Users completed
113 done
Explain the Observer pattern and its use cases
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Easy
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JavaScript
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87 done
How can closures be used to create private variables?
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Easy
Topics
Closure
JavaScript
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111 done
How can you avoid problems related to hoisting?
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Easy
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JavaScript
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103 done
How can you create custom error objects?
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Easy
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JavaScript
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91 done
How can you implement secure authentication and authorization in JavaScript applications?
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Easy
Topics
JavaScript
Security
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113 done
How can you optimize DOM manipulation for better performance?
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Easy
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Web APIs
JavaScript
Performance
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121 done
How can you optimize network requests for better performance?
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Easy
Topics
JavaScript
Networking
Performance
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122 done
How can you prevent clickjacking attacks?
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Easy
Topics
JavaScript
Security
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106 done
How can you prevent SQL injection vulnerabilities in JavaScript applications?
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Difficulty
Easy
Topics
JavaScript
Security
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103 done
How can you test asynchronous code in JavaScript?
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Difficulty
Easy
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Async
JavaScript
Testing
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118 done
How do currying and partial application differ from each other?
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Difficulty
Easy
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Closure
JavaScript
Users completed
95 done
How do `<iframe>` on a page communicate?
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Easy
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Web APIs
JavaScript
HTML
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126 done
How do `Set`s and `Map`s handle equality checks for objects?
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Easy
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JavaScript
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88 done
How do you access the index of an element in an array during iteration?
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Easy
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JavaScript
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96 done
How do you add, remove, and modify HTML elements using JavaScript?
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Easy
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Web APIs
JavaScript
HTML
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128 done
How do you add, remove, and update elements in an array?
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Easy
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JavaScript
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98 done
How do you check if an object has a specific property?
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Easy
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JavaScript
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100 done
How do you check the data type of a variable?
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Easy
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JavaScript
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98 done
How do you convert a `Set` to an array in JavaScript?
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Easy
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JavaScript
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96 done
How do you convert a string to a number in JavaScript?
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Easy
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JavaScript
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105 done
How do you create a constructor function?
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Easy
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JavaScript
OOP
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97 done
How do you detect if JavaScript is disabled on a page?
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Difficulty
Easy
Topics
Browser
JavaScript
Users completed
92 done
How do you get the query string values of the current page in JavaScript?
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Easy
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Web APIs
JavaScript
Users completed
81 done
How do you handle errors in asynchronous operations?
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Difficulty
Easy
Topics
Async
JavaScript
Users completed
97 done
How do you handle errors using `try...catch` blocks?
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Easy
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JavaScript
Users completed
94 done
How do you import and export modules in JavaScript?
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Easy
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JavaScript
Users completed
87 done
How do you make an HTTP request using the Fetch API?
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Easy
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JavaScript
Networking
Users completed
109 done
How do you manipulate CSS styles using JavaScript?
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Easy
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CSS
Web APIs
JavaScript
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121 done
How do you prevent the default behavior of an event?
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Easy
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Web APIs
JavaScript
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97 done
How do you redirect to a new page in JavaScript?
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Difficulty
Easy
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Web APIs
JavaScript
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86 done
How do you reliably determine whether an object is empty?
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Easy
Topics
JavaScript
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93 done
How do you use `window.history` API?
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Easy
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Web APIs
JavaScript
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75 done
How do you validate form elements using the Constraint Validation API?
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Easy
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Web APIs
JavaScript
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65 done
How do you write unit tests for JavaScript code?
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Easy
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JavaScript
Testing
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91 done
How does hoisting affect function declarations and expressions?
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Easy
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JavaScript
Users completed
85 done
How is `Promise.all()` different from `Promise.allSettled()`?
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Easy
Topics
Async
JavaScript
Users completed
105 done
Provide some examples of how currying and partial application can be used
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Easy
Topics
Closure
JavaScript
Users completed
82 done
What are callback functions and how are they used?
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Difficulty
Easy
Topics
Async
JavaScript
Users completed
96 done
What are default parameters and how are they used?
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Easy
Topics
JavaScript
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86 done
What are design patterns and why are they useful?
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Difficulty
Easy
Topics
JavaScript
Users completed
76 done
What are event listeners and how are they used?
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Difficulty
Easy
Topics
Web APIs
JavaScript
Users completed
86 done
What are mocks and stubs and how are they used in testing?
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Difficulty
Easy
Topics
JavaScript
Testing
Users completed
75 done
What are modules and why are they useful?
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Difficulty
Easy
Topics
JavaScript
Users completed
79 done
What are Progressive Web Applications (PWAs)?
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Difficulty
Easy
Topics
Browser
JavaScript
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76 done
What are Promises and how do they work?
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Difficulty
Easy
Topics
JavaScript
Users completed
118 done
What are rest parameters and how are they used?
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Easy
Topics
JavaScript
Users completed
83 done
What are `Set`s and `Map`s and how are they used?
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Difficulty
Easy
Topics
JavaScript
Users completed
82 done
What are some best practices for handling sensitive data in JavaScript?
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Difficulty
Easy
Topics
JavaScript
Security
Users completed
96 done
What are some best practices for writing maintainable and effective tests in JavaScript?
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Difficulty
Easy
Topics
JavaScript
Testing
Users completed
83 done
What are some common performance bottlenecks in JavaScript applications?
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Easy
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JavaScript
Performance
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101 done
What are some common security headers and their purpose?
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Easy
Topics
JavaScript
Security
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79 done
What are some popular JavaScript testing frameworks?
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Easy
Topics
JavaScript
Testing
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83 done
What are some techniques for reducing reflows and repaints?
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Difficulty
Easy
Topics
Browser
JavaScript
Performance
Users completed
89 done
What are some tools and techniques for identifying security vulnerabilities in JavaScript code?
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Difficulty
Easy
Topics
JavaScript
Security
Users completed
84 done
What are some tools that can be used for JavaScript testing?
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Difficulty
Easy
Topics
JavaScript
Testing
Users completed
79 done
What are some tools that can be used to measure and analyze JavaScript performance?
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Difficulty
Easy
Topics
JavaScript
Performance
Users completed
93 done
What are template literals and how are they used?
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Difficulty
Easy
Topics
JavaScript
Users completed
78 done
What are the advantages of using the spread operator with arrays and objects?
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Difficulty
Easy
Topics
JavaScript
Users completed
80 done
What are the benefits of using a module bundler?
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Difficulty
Easy
Topics
JavaScript
Users completed
73 done
What are the benefits of using currying and partial application?
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Difficulty
Easy
Topics
Closure
JavaScript
Users completed
73 done
What are the common pitfalls of using the `this` keyword?
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Difficulty
Easy
Topics
JavaScript
OOP
Users completed
75 done
What are the different methods for iterating over an array?
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Difficulty
Easy
Topics
JavaScript
Users completed
80 done
What are the different types of errors in JavaScript?
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Difficulty
Easy
Topics
JavaScript
Users completed
77 done
What are the different types of testing in software development?
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Difficulty
Easy
Topics
JavaScript
Testing
Users completed
82 done
What are the different ways to copy an object or an array?
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Difficulty
Easy
Topics
JavaScript
Users completed
81 done
What are the different ways to make an API call in JavaScript?
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Difficulty
Easy
Topics
JavaScript
Networking
Users completed
91 done
What are the metadata fields of a module?
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Difficulty
Easy
Topics
JavaScript
Users completed
66 done
What are the potential issues caused by hoisting?
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Difficulty
Easy
Topics
JavaScript
Users completed
78 done
What are the potential pitfalls of using closures?
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Difficulty
Easy
Topics
Closure
JavaScript
Users completed
86 done
What are Web Workers and how can they be used to improve performance?
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Difficulty
Easy
Topics
Web APIs
JavaScript
Performance
Users completed
94 done
What is async/await and how does it simplify asynchronous code?
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Difficulty
Easy
Topics
Async
JavaScript
Users completed
97 done
What is Cross-Site Scripting (XSS) and how can you prevent it?
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Difficulty
Easy
Topics
JavaScript
Security
Users completed
105 done
What is currying and how does it work?
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Difficulty
Easy
Topics
Closure
JavaScript
Users completed
91 done
What is `Object.freeze()` for?
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Difficulty
Easy
Topics
JavaScript
Users completed
81 done
What is `Object.preventExtensions()` for?
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Difficulty
Easy
Topics
JavaScript
Users completed
69 done
What is `Object.seal()` for?
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Difficulty
Easy
Topics
JavaScript
Users completed
74 done
What is recursion and how is it used in JavaScript?
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Difficulty
Easy
Topics
JavaScript
Recursion
Users completed
78 done
What is the Command pattern and how is it used?
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Difficulty
Easy
Topics
JavaScript
Users completed
58 done
What is the Decorator pattern and how is it used?
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Difficulty
Easy
Topics
JavaScript
Users completed
62 done
What is the difference between a parameter and an argument?
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Difficulty
Easy
Topics
JavaScript
Users completed
84 done
What is the difference between `event.preventDefault()` and `event.stopPropagation()`?
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Quiz
Difficulty
Easy
Topics
Web APIs
HTML
JavaScript
Users completed
133 done
What is the difference between `innerHTML` and `textContent`?
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Difficulty
Easy
Topics
Web APIs
HTML
JavaScript
Users completed
125 done
What is the difference between `setTimeout()`, `setImmediate()`, and `process.nextTick()`?
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Difficulty
Easy
Topics
Web APIs
JavaScript
Users completed
70 done
What is the difference between the Window object and the Document object?
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Difficulty
Easy
Topics
Web APIs
JavaScript
Users completed
85 done
What is the DOM and how is it structured?
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Difficulty
Easy
Topics
JavaScript
HTML
Users completed
136 done
What is the Factory pattern and how is it used?
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Difficulty
Easy
Topics
JavaScript
Users completed
68 done
What is the `Intl` namespace object for?
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Difficulty
Easy
Topics
JavaScript
Internationalization
Users completed
88 done
What is the Module pattern and how does it help with encapsulation?
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Difficulty
Easy
Topics
JavaScript
Users completed
71 done
What is the prototype chain and how does it work?
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Difficulty
Easy
Topics
JavaScript
OOP
Users completed
94 done
What is the purpose of the `break` and `continue` statements?
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Difficulty
Easy
Topics
JavaScript
Users completed
101 done
What is the purpose of the `finally` block?
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Difficulty
Easy
Topics
JavaScript
Users completed
101 done
What is the purpose of the `new` keyword?
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Difficulty
Easy
Topics
JavaScript
OOP
Users completed
90 done
What is the purpose of the `switch` statement?
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Easy
Topics
JavaScript
Users completed
114 done
What is the spread operator and how is it used?
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Difficulty
Easy
Topics
JavaScript
Users completed
121 done
What is the ternary operator and how is it used?
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Difficulty
Easy
Topics
JavaScript
Users completed
120 done
What is the use of `Promise.all()`
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Difficulty
Easy
Topics
Async
JavaScript
Users completed
150 done
What's the difference between an "attribute" and a "property" in the DOM?
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Difficulty
Easy
Topics
Web APIs
JavaScript
HTML
Users completed
752 done
What are the differences between JavaScript variables created using `let`, `var` or `const`?
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Difficulty
Medium
Topics
JavaScript
Users completed
3.48k done
Explain event delegation in JavaScript
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Difficulty
Medium
Topics
Web APIs
JavaScript
Users completed
2.5k done
Describe the difference between a cookie, `sessionStorage` and `localStorage` in browsers
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Difficulty
Medium
Topics
Web APIs
JavaScript
Users completed
2.92k done
Describe the difference between `<script>`, `<script async>` and `<script defer>`
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Quiz
Difficulty
Medium
Topics
HTML
JavaScript
Users completed
4.03k done
What's the difference between feature detection, feature inference, and using the UA string?
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Difficulty
Medium
Topics
Browser
JavaScript
Users completed
620 done
Explain `Function.prototype.bind` in JavaScript
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Quiz
Difficulty
Medium
Topics
JavaScript
OOP
Users completed
1.97k done
What advantage is there for using the JavaScript arrow syntax for a method in a constructor?
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Difficulty
Medium
Topics
JavaScript
Users completed
845 done
Explain how prototypal inheritance works in JavaScript
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Difficulty
Medium
Topics
JavaScript
OOP
Users completed
2.8k done
Difference between: `function Person(){}`, `const person = Person()`, and `const person = new Person()` in JavaScript?
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Quiz
Difficulty
Medium
Topics
JavaScript
OOP
Users completed
1.14k done
Explain the differences on the usage of `foo` between `function foo() {}` and `var foo = function() {}` in JavaScript
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Quiz
Difficulty
Medium
Topics
JavaScript
Users completed
999 done
What's a typical use case for anonymous functions in JavaScript?
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Difficulty
Medium
Topics
JavaScript
Users completed
1.75k done
What are the various ways to create objects in JavaScript?
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Difficulty
Medium
Topics
JavaScript
Users completed
656 done
What is a closure in JavaScript, and how/why would you use one?
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Quiz
Difficulty
Medium
Topics
Closure
JavaScript
Users completed
1.96k done
What is the definition of a higher-order function in JavaScript?
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Difficulty
Medium
Topics
JavaScript
Users completed
882 done
Describe event bubbling in JavaScript and browsers
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Difficulty
Medium
Topics
Web APIs
JavaScript
Users completed
2.35k done
Describe event capturing in JavaScript and browsers
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Difficulty
Medium
Topics
Web APIs
JavaScript
Users completed
796 done
Explain the difference between synchronous and asynchronous functions in JavaScript
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Quiz
Difficulty
Medium
Topics
Async
JavaScript
Users completed
1.9k done
What are the pros and cons of using Promises instead of callbacks in JavaScript?
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Difficulty
Medium
Topics
Async
JavaScript
Users completed
1.93k done
What are JavaScript polyfills for?
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Difficulty
Medium
Topics
JavaScript
Users completed
239 done
Why is extending built-in JavaScript objects not a good idea?
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