Javascript Fundamentals Practice Exam

Question 1 Javascript Fundamentals

Who created JavaScript and in what year?

Optional chaining (?.) safely reads nested properties or calls methods without throwing when an intermediate value is null or undefined. async functions return Promises; await pauses until Promise settles, e.g., const data = await fetch(url);. Use try/catch for errors. JavaScript was created by Brendan Eich in 1995 while working at Netscape. It was initially called Mocha, then LiveScript, before being renamed JavaScript. null represents an intentional absence of value, while undefined means a variable has been declared but not assigned. typeof null is 'object', a historical bug.

Question 2 Javascript Fundamentals

How do you create an array?

It keeps async workflows predictable and prevents deeply nested callbacks. Arrays are created with [], e.g., const arr = [1, 'a', true]; or new Array(). They are zero-indexed. A for loop has for (init; condition; increment) { ... }, e.g., for (let i=0; i<5; i++). Init runs once, condition checks each iteration. A simple example is using lexical scope in a small project, note, or decision before applying it to a larger real-world situation.

Question 3 Javascript Fundamentals

What is a common mistake with immutability?

Mutating arrays or objects directly and expecting change detection to work. filter() creates a new array with elements passing a test, e.g., [1,2,3].filter(x => x>1) returns [2,3]. Returns boolean from callback. map() creates a new array with results of calling a function on each element, e.g., [1,2].map(x => x*2) returns [2,4]. Doesn't mutate original. A simple example is using async error handling in a small project, note, or decision before applying it to a larger real-world situation.

Question 4 Javascript Fundamentals

How do you check the type of a value?

Variables can be declared using var (function-scoped), let (block-scoped), or const (block-scoped constant). let and const were introduced in ES6. Math is a built-in object with no constructor, providing Math.random(), Math.floor(), Math.PI, etc., for math operations. Use the typeof operator, e.g., typeof 'hello' returns 'string'. It returns a string describing the type. Use dot notation obj.prop or bracket obj['prop']. Bracket allows dynamic keys like variables.

Question 5 Javascript Fundamentals

What is a common mistake with strict mode?

Assuming all old JavaScript behavior remains valid under strict mode. JavaScript was created by Brendan Eich in 1995 while working at Netscape. It was initially called Mocha, then LiveScript, before being renamed JavaScript. The primitive types are string, number, bigint, boolean, undefined, null, and symbol. They are immutable basic values. A module is a file that can export and import values using export and import, helping organize code and avoid global namespace pollution.

Question 6 Javascript Fundamentals

What question should you ask when using event delegation?

A simple example is using prototype chain in a small project, note, or decision before applying it to a larger real-world situation. 'this' refers to the execution context object. In global scope it's window (browser); in methods it's the object; arrow functions inherit from parent. Ask: what problem is this solving, what trade-off does it create, and how will I know it worked? It catches mistakes such as accidental globals and unsafe assignments.

Question 7 Javascript Fundamentals

What question should you ask when using async error handling?

A switch statement evaluates an expression and executes code matching a case value, using break to exit. It supports default for no match. Ask: what problem is this solving, what trade-off does it create, and how will I know it worked? Comparison operators like ==, ===, !=, !==, >, etc., return a boolean (true or false). === checks value and type. JavaScript was created by Brendan Eich in 1995 while working at Netscape. It was initially called Mocha, then LiveScript, before being renamed JavaScript.

Question 8 Javascript Fundamentals

How can you practice Promise chaining?

Debouncing delays a function call until a quiet period has passed, commonly used for search inputs so an API call is not made on every keystroke. Destructuring extracts values from arrays/objects into variables, e.g., const [a, b] = [1, 2]; or const {x} = {x: 10};. ES6 feature. Math is a built-in object with no constructor, providing Math.random(), Math.floor(), Math.PI, etc., for math operations. Apply it to a small realistic example, explain the decision out loud, then check whether the result matches the intended outcome.

Question 9 Javascript Fundamentals

What is the Math object?

Math is a built-in object with no constructor, providing Math.random(), Math.floor(), Math.PI, etc., for math operations. JavaScript was created by Brendan Eich in 1995 while working at Netscape. It was initially called Mocha, then LiveScript, before being renamed JavaScript. Promise chaining sequences asynchronous steps by returning values or promises from .then() callbacks. Mutating arrays or objects directly and expecting change detection to work.

Question 10 Javascript Fundamentals

What does the nullish coalescing operator do?

A module is a file that can export and import values using export and import, helping organize code and avoid global namespace pollution. Debouncing delays a function call until a quiet period has passed, commonly used for search inputs so an API call is not made on every keystroke. ?? returns the fallback only when the left side is null or undefined, unlike || which also treats 0, '', and false as fallback cases. Logical operators are && (AND), || (OR), and ! (NOT). They perform boolean logic and enable short-circuit evaluation.

Question 11 Javascript Fundamentals

What is a simple example of Promise chaining?

A switch statement evaluates an expression and executes code matching a case value, using break to exit. It supports default for no match. A simple example is using promise chaining in a small project, note, or decision before applying it to a larger real-world situation. 'this' refers to the execution context object. In global scope it's window (browser); in methods it's the object; arrow functions inherit from parent. Promises represent eventual completion/failure of async operations, with .then(), .catch(). States: pending, fulfilled, rejected.

Question 12 Javascript Fundamentals

What does async error handling mean in JavaScript fundamentals?

Async error handling uses try/catch around await or .catch() on promises. async functions return Promises; await pauses until Promise settles, e.g., const data = await fetch(url);. Use try/catch for errors. map() creates a new array with results of calling a function on each element, e.g., [1,2].map(x => x*2) returns [2,4]. Doesn't mutate original. A simple example is using prototype chain in a small project, note, or decision before applying it to a larger real-world situation.

Question 13 Javascript Fundamentals

What are default parameters?

Use dot notation obj.prop or bracket obj['prop']. Bracket allows dynamic keys like variables. The if statement executes code if a condition is truthy; else if checks alternatives; else runs if all fail. Conditions coerce to boolean. Default parameters set fallback values, e.g., function greet(name = 'World') {}. Evaluated if undefined. Lexical scope means a function can access variables based on where it was written in the source code.

Question 14 Javascript Fundamentals

How do you work with the Date object?

Assuming scope depends on where a function is called instead of where it is defined. JavaScript was created by Brendan Eich in 1995 while working at Netscape. It was initially called Mocha, then LiveScript, before being renamed JavaScript. Microtasks are high-priority async callbacks such as promise callbacks that run after the current stack before many macrotasks. Create with new Date() for current time or new Date('2023-01-01'). Methods: getFullYear(), setHours(), etc.

Question 15 Javascript Fundamentals

What is JavaScript scope?

Confusing prototypes with classical classes in languages like Java or C#. It improves performance and works well for dynamically added elements. Adding separate listeners to hundreds of child nodes when one parent listener would work. Scope determines variable accessibility. Global scope is outermost; function scope (var) or block scope (let/const) limits to their block.

Question 16 Javascript Fundamentals

What is 'use strict'?

Throttling ensures a function runs at most once in a defined interval, useful for scroll, resize, and mouse-move handlers. ?? returns the fallback only when the left side is null or undefined, unlike || which also treats 0, '', and false as fallback cases. 'use strict'; enables strict mode, enforcing better practices like no undeclared variables or duplicate parameters. It's a string literal at script/function top. Variables can be declared using var (function-scoped), let (block-scoped), or const (block-scoped constant). let and const were introduced in ES6.

Question 17 Javascript Fundamentals

How can you practice strict mode?

'this' refers to the execution context object. In global scope it's window (browser); in methods it's the object; arrow functions inherit from parent. A rest parameter (...args) collects multiple function arguments into a single array-like variable. Apply it to a small realistic example, explain the decision out loud, then check whether the result matches the intended outcome. Parameters are variables in the function definition; arguments are values passed when calling. Functions can access arguments object for all passed values.

Question 18 Javascript Fundamentals

What is JavaScript?

It makes state changes easier to reason about in UI frameworks and reducers. A simple example is using event delegation in a small project, note, or decision before applying it to a larger real-world situation. JavaScript is a high-level, interpreted programming language primarily used for web development to make web pages interactive. It is the scripting language of the Web, supported by all modern browsers, and follows the ECMAScript specification. Microtasks are high-priority async callbacks such as promise callbacks that run after the current stack before many macrotasks.

Question 19 Javascript Fundamentals

What are the ways to declare variables in JavaScript?

Variables can be declared using var (function-scoped), let (block-scoped), or const (block-scoped constant). let and const were introduced in ES6. It improves performance and works well for dynamically added elements. It explains inheritance, methods, and why objects can share behavior. Spread ... expands iterables, e.g., const newArr = [...oldArr, 1]; for shallow copy or Math.max(...nums) for function args.

Question 20 Javascript Fundamentals

Why does async error handling matter in JavaScript fundamentals?

It prevents failed requests or rejected promises from silently breaking user flows. Use function name(parameters) { ... } for declarations, hoisted at runtime. Expressions like const func = function() {} are not hoisted. Use document.getElementById('id'), document.querySelector('.class'), or document.querySelectorAll(). Returns Element or NodeList. JavaScript is a high-level, interpreted programming language primarily used for web development to make web pages interactive. It is the scripting language of the Web, supported by all modern browsers, and follows the ECMAScript specification.

Question 21 Javascript Fundamentals

How do you define a class in ES6?

Lexical scope means a function can access variables based on where it was written in the source code. Hoisting moves variable and function declarations to the top of their scope before execution. var is hoisted with undefined; let/const have Temporal Dead Zone. Use class MyClass { constructor(props) { this.props = props; } method() {} }. Syntactic sugar over prototypes. A rest parameter (...args) collects multiple function arguments into a single array-like variable.

Question 22 Javascript Fundamentals

What does immutability mean in JavaScript fundamentals?

It catches mistakes such as accidental globals and unsafe assignments. The prototype chain is how JavaScript looks up properties on an object and then on its prototypes. A for loop has for (init; condition; increment) { ... }, e.g., for (let i=0; i<5; i++). Init runs once, condition checks each iteration. Immutability means creating new values instead of changing existing ones.

Question 23 Javascript Fundamentals

What is a simple example of lexical scope?

Use dot notation obj.prop or bracket obj['prop']. Bracket allows dynamic keys like variables. The prototype chain is how JavaScript looks up properties on an object and then on its prototypes. ?? returns the fallback only when the left side is null or undefined, unlike || which also treats 0, '', and false as fallback cases. A simple example is using lexical scope in a small project, note, or decision before applying it to a larger real-world situation.

Question 24 Javascript Fundamentals

What is an object literal?

It explains closures, module patterns, and why functions can remember outer variables. Assuming scope depends on where a function is called instead of where it is defined. A pure function always returns the same output for the same input and does not create side effects such as changing external state or making network calls. An object literal is { key: value }, e.g., const obj = {name: 'JS'};. Keys are strings or symbols, values any type.

Question 25 Javascript Fundamentals

What does console.log() do?

Adding separate listeners to hundreds of child nodes when one parent listener would work. console.log() outputs a message to the browser's console for debugging and logging. It can log multiple arguments of any type, like console.log('Hello', 42);. while checks condition before executing; do-while executes once then checks. do-while guarantees at least one iteration. Confusing prototypes with classical classes in languages like Java or C#.

Question 26 Javascript Fundamentals

What is the difference between == and ===?

A pure function always returns the same output for the same input and does not create side effects such as changing external state or making network calls. Parameters are variables in the function definition; arguments are values passed when calling. Functions can access arguments object for all passed values. == coerces types before comparing; === checks value and type strictly. Prefer === to avoid bugs. Adding separate listeners to hundreds of child nodes when one parent listener would work.

Question 27 Javascript Fundamentals

What is an event listener?

Throttling ensures a function runs at most once in a defined interval, useful for scroll, resize, and mouse-move handlers. Mutating arrays or objects directly and expecting change detection to work. Event listeners respond to DOM events like clicks: element.addEventListener('click', handler). Can remove with removeEventListener(). ?? returns the fallback only when the left side is null or undefined, unlike || which also treats 0, '', and false as fallback cases.

Question 28 Javascript Fundamentals

What does prototype chain mean in JavaScript fundamentals?

JavaScript is a high-level, interpreted programming language primarily used for web development to make web pages interactive. It is the scripting language of the Web, supported by all modern browsers, and follows the ECMAScript specification. A switch statement evaluates an expression and executes code matching a case value, using break to exit. It supports default for no match. The prototype chain is how JavaScript looks up properties on an object and then on its prototypes. Spread ... expands iterables, e.g., const newArr = [...oldArr, 1]; for shallow copy or Math.max(...nums) for function args.

Question 29 Javascript Fundamentals

Why does strict mode matter in JavaScript fundamentals?

Spread ... expands iterables, e.g., const newArr = [...oldArr, 1]; for shallow copy or Math.max(...nums) for function args. It catches mistakes such as accidental globals and unsafe assignments. A simple example is using strict mode in a small project, note, or decision before applying it to a larger real-world situation. Use dot notation obj.prop or bracket obj['prop']. Bracket allows dynamic keys like variables.

Question 30 Javascript Fundamentals

What is JSON?

JSON (JavaScript Object Notation) is a text format for data interchange, like {"name": "JS"}. Use JSON.parse() to object, JSON.stringify() to string. Mutating arrays or objects directly and expecting change detection to work. Use extends and super(), e.g., class Child extends Parent { constructor() { super(); } }. Calls parent constructor. Scope determines variable accessibility. Global scope is outermost; function scope (var) or block scope (let/const) limits to their block.

Question 31 Javascript Fundamentals

What is an IIFE?

JavaScript is a high-level, interpreted programming language primarily used for web development to make web pages interactive. It is the scripting language of the Web, supported by all modern browsers, and follows the ECMAScript specification. Mutating arrays or objects directly and expecting change detection to work. The return statement exits the function and sends a value back to the caller. Without it, functions return undefined. Immediately Invoked Function Expression (IIFE) is (function() { ... })();. It runs instantly, creating private scope to avoid globals.

Question 32 Javascript Fundamentals

What is a common mistake with prototype chain?

Microtasks are high-priority async callbacks such as promise callbacks that run after the current stack before many macrotasks. Assuming scope depends on where a function is called instead of where it is defined. Confusing prototypes with classical classes in languages like Java or C#. An object literal is { key: value }, e.g., const obj = {name: 'JS'};. Keys are strings or symbols, values any type.

Question 33 Javascript Fundamentals

Why does event delegation matter in JavaScript fundamentals?

It improves performance and works well for dynamically added elements. push() adds to end, pop() removes from end, shift() from start, unshift() adds to start. They mutate the array. Mutating arrays or objects directly and expecting change detection to work. It keeps async workflows predictable and prevents deeply nested callbacks.

Question 34 Javascript Fundamentals

How do you access object properties?

async functions return Promises; await pauses until Promise settles, e.g., const data = await fetch(url);. Use try/catch for errors. Debouncing delays a function call until a quiet period has passed, commonly used for search inputs so an API call is not made on every keystroke. Use the typeof operator, e.g., typeof 'hello' returns 'string'. It returns a string describing the type. Use dot notation obj.prop or bracket obj['prop']. Bracket allows dynamic keys like variables.

Question 35 Javascript Fundamentals

What are Promises?

Promises represent eventual completion/failure of async operations, with .then(), .catch(). States: pending, fulfilled, rejected. Use extends and super(), e.g., class Child extends Parent { constructor() { super(); } }. Calls parent constructor. Destructuring extracts values from arrays/objects into variables, e.g., const [a, b] = [1, 2]; or const {x} = {x: 10};. ES6 feature. Wrapping only synchronous code and missing rejected promises.

Question 36 Javascript Fundamentals

What is a closure?

A simple example is using immutability in a small project, note, or decision before applying it to a larger real-world situation. Template literals use backticks `Hello ${name}` for strings with embedded expressions. They support multi-line strings and tagged templates. A closure is a function that retains access to its outer scope's variables even after the outer function finishes. Useful for data privacy and modules. ECMAScript (ES) is the standardized scripting language specification upon which JavaScript is based. The latest stable version is ES2023, with JavaScript implementing all ES features plus browser-specific ones.

Question 37 Javascript Fundamentals

What is hoisting?

Math is a built-in object with no constructor, providing Math.random(), Math.floor(), Math.PI, etc., for math operations. reduce() applies a function against accumulator and each element, reducing to single value, e.g., sum: [1,2].reduce((a,b)=>a+b, 0). JavaScript was created by Brendan Eich in 1995 while working at Netscape. It was initially called Mocha, then LiveScript, before being renamed JavaScript. Hoisting moves variable and function declarations to the top of their scope before execution. var is hoisted with undefined; let/const have Temporal Dead Zone.

Question 38 Javascript Fundamentals

How can you practice async error handling?

'use strict'; enables strict mode, enforcing better practices like no undeclared variables or duplicate parameters. It's a string literal at script/function top. Throttling ensures a function runs at most once in a defined interval, useful for scroll, resize, and mouse-move handlers. Apply it to a small realistic example, explain the decision out loud, then check whether the result matches the intended outcome. Forgetting to return a promise, causing the next step to run too early.

Question 39 Javascript Fundamentals

What methods add/remove from arrays?

Mutating arrays or objects directly and expecting change detection to work. push() adds to end, pop() removes from end, shift() from start, unshift() adds to start. They mutate the array. Variables can be declared using var (function-scoped), let (block-scoped), or const (block-scoped constant). let and const were introduced in ES6. while checks condition before executing; do-while executes once then checks. do-while guarantees at least one iteration.

Question 40 Javascript Fundamentals

Describe the for loop syntax.

The call stack tracks function execution order, LIFO. Browsers use it with event loop for async tasks like setTimeout. A for loop has for (init; condition; increment) { ... }, e.g., for (let i=0; i<5; i++). Init runs once, condition checks each iteration. filter() creates a new array with elements passing a test, e.g., [1,2,3].filter(x => x>1) returns [2,3]. Returns boolean from callback. The if statement executes code if a condition is truthy; else if checks alternatives; else runs if all fail. Conditions coerce to boolean.

Question 41 Javascript Fundamentals

What does event delegation mean in JavaScript fundamentals?

Immutability means creating new values instead of changing existing ones. == coerces types before comparing; === checks value and type strictly. Prefer === to avoid bugs. Event delegation attaches one listener to a parent and handles events from child elements through bubbling. Default parameters set fallback values, e.g., function greet(name = 'World') {}. Evaluated if undefined.

Question 42 Javascript Fundamentals

How does the if-else statement work?

Use class MyClass { constructor(props) { this.props = props; } method() {} }. Syntactic sugar over prototypes. A simple example is using strict mode in a small project, note, or decision before applying it to a larger real-world situation. The return statement exits the function and sends a value back to the caller. Without it, functions return undefined. The if statement executes code if a condition is truthy; else if checks alternatives; else runs if all fail. Conditions coerce to boolean.

Question 43 Javascript Fundamentals

What is a common mistake with event delegation?

Optional chaining (?.) safely reads nested properties or calls methods without throwing when an intermediate value is null or undefined. Adding separate listeners to hundreds of child nodes when one parent listener would work. It keeps async workflows predictable and prevents deeply nested callbacks. Spread ... expands iterables, e.g., const newArr = [...oldArr, 1]; for shallow copy or Math.max(...nums) for function args.

Question 44 Javascript Fundamentals

What does the return statement do?

The return statement exits the function and sends a value back to the caller. Without it, functions return undefined. The if statement executes code if a condition is truthy; else if checks alternatives; else runs if all fail. Conditions coerce to boolean. A closure is a function that retains access to its outer scope's variables even after the outer function finishes. Useful for data privacy and modules. Mutating arrays or objects directly and expecting change detection to work.

Question 45 Javascript Fundamentals

What are rest parameters?

Use function name(parameters) { ... } for declarations, hoisted at runtime. Expressions like const func = function() {} are not hoisted. A simple example is using async error handling in a small project, note, or decision before applying it to a larger real-world situation. Template literals use backticks `Hello ${name}` for strings with embedded expressions. They support multi-line strings and tagged templates. Rest ...args collects remaining arguments into an array, e.g., function sum(...nums) {}. Only last parameter.

Question 46 Javascript Fundamentals

How does async/await work?

Arrays are created with [], e.g., const arr = [1, 'a', true]; or new Array(). They are zero-indexed. Throttling ensures a function runs at most once in a defined interval, useful for scroll, resize, and mouse-move handlers. async functions return Promises; await pauses until Promise settles, e.g., const data = await fetch(url);. Use try/catch for errors. A closure is a function that retains access to its outer scope's variables even after the outer function finishes. Useful for data privacy and modules.

Question 47 Javascript Fundamentals

What is Array.prototype.reduce()?

JSON (JavaScript Object Notation) is a text format for data interchange, like {"name": "JS"}. Use JSON.parse() to object, JSON.stringify() to string. reduce() applies a function against accumulator and each element, reducing to single value, e.g., sum: [1,2].reduce((a,b)=>a+b, 0). map() creates a new array with results of calling a function on each element, e.g., [1,2].map(x => x*2) returns [2,4]. Doesn't mutate original. Scope determines variable accessibility. Global scope is outermost; function scope (var) or block scope (let/const) limits to their block.

Question 48 Javascript Fundamentals

What are JavaScript's primitive data types?

Math is a built-in object with no constructor, providing Math.random(), Math.floor(), Math.PI, etc., for math operations. It explains closures, module patterns, and why functions can remember outer variables. JSON (JavaScript Object Notation) is a text format for data interchange, like {"name": "JS"}. Use JSON.parse() to object, JSON.stringify() to string. The primitive types are string, number, bigint, boolean, undefined, null, and symbol. They are immutable basic values.

Question 49 Javascript Fundamentals

What is the difference between while and do-while loops?

The event object (e) passed to handlers contains event details like e.target, e.preventDefault() to stop default behavior. Use dot notation obj.prop or bracket obj['prop']. Bracket allows dynamic keys like variables. JavaScript was created by Brendan Eich in 1995 while working at Netscape. It was initially called Mocha, then LiveScript, before being renamed JavaScript. while checks condition before executing; do-while executes once then checks. do-while guarantees at least one iteration.

Question 50 Javascript Fundamentals

What is a pure function?

A pure function always returns the same output for the same input and does not create side effects such as changing external state or making network calls. A simple example is using async error handling in a small project, note, or decision before applying it to a larger real-world situation. Variables can be declared using var (function-scoped), let (block-scoped), or const (block-scoped constant). let and const were introduced in ES6. Create with new Date() for current time or new Date('2023-01-01'). Methods: getFullYear(), setHours(), etc.