JavaScript Overview and Features
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Questions and Answers

The script tag can be placed in the head of an HTML file, which improves the page loading time.

True (A)

The script tag can be placed in the head of an HTML file, however, doing so may affect the page's appearance until the JavaScript is loaded.

True (A)

A variable declared with let has function scope.

False (B)

The console.log() function can be used to print the values of variables to the console.

<p>True (A)</p> Signup and view all the answers

JavaScript code is compiled by the browser.

<p>False (B)</p> Signup and view all the answers

JavaScript code can be written directly in the HTML file, using the script tag.

<p>True (A)</p> Signup and view all the answers

The document.write() function is a preferred method for outputting dynamic content for modern web development.

<p>False (B)</p> Signup and view all the answers

JavaScript code can be executed from bottom to top (reverse order) using the reverse() function.

<p>False (B)</p> Signup and view all the answers

The alert() function is used to display a pop-up message on the user's screen, and the console.log() function is used to display the messages in the browser's console.

<p>True (A)</p> Signup and view all the answers

ECMAScript 2015 (ES6) does not support promises.

<p>False (B)</p> Signup and view all the answers

The Fetch API replaces XMLHttpRequest (AJAX style) for making network requests.

<p>True (A)</p> Signup and view all the answers

Let and const keywords have the same scope as var.

<p>False (B)</p> Signup and view all the answers

Arrow functions are also referred to as lambdas.

<p>True (A)</p> Signup and view all the answers

JavaScript is only used on about 5% of websites.

<p>False (B)</p> Signup and view all the answers

React is a very popular framework, gaining popularity in StackOverflow's 2024 Developer Survey.

<p>True (A)</p> Signup and view all the answers

TypeScript is an interpreted language.

<p>False (B)</p> Signup and view all the answers

JavaScript can be classified as a high-level language.

<p>True (A)</p> Signup and view all the answers

Javascript is not dynamic, as it is an interpreted language.

<p>False (B)</p> Signup and view all the answers

JavaScript is classified as a strongly typed language.

<p>False (B)</p> Signup and view all the answers

The for...in loop can be used with lists.

<p>False (B)</p> Signup and view all the answers

JavaScript execution in the browser is primarily driven by events.

<p>True (A)</p> Signup and view all the answers

An event handler is a function that executes when a specific event occurs.

<p>True (A)</p> Signup and view all the answers

The DOM represents a flat structure of HTML elements.

<p>False (B)</p> Signup and view all the answers

The for...of loop can be used with objects.

<p>False (B)</p> Signup and view all the answers

You can modify the DOM by adding or removing nodes.

<p>True (A)</p> Signup and view all the answers

Every element of a web page is inaccessible to JavaScript.

<p>False (B)</p> Signup and view all the answers

A click on a button emits a 'click' event.

<p>True (A)</p> Signup and view all the answers

The function hello() is called before it is defined due to hoisting.

<p>True (A)</p> Signup and view all the answers

Variables defined with 'let' have function-level scope.

<p>False (B)</p> Signup and view all the answers

The statement 'console.log(y);' outputs a value when y is declared with 'const' inside an if block.

<p>False (B)</p> Signup and view all the answers

Using 'var', a variable is accessible outside of the function in which it was declared.

<p>False (B)</p> Signup and view all the answers

The output of the function hello() includes the messages 'Hello!' and 'Welcome to JavaScript'.

<p>True (A)</p> Signup and view all the answers

Letting a variable go out of scope after a loop is the same as using 'var'.

<p>False (B)</p> Signup and view all the answers

In JavaScript, functions declared in the global scope are accessible from anywhere in the code.

<p>True (A)</p> Signup and view all the answers

Hoisting can lead to unexpected behaviors and is not a good practice.

<p>True (A)</p> Signup and view all the answers

The const keyword in JavaScript allows reassignment of variables.

<p>False (B)</p> Signup and view all the answers

Null represents a value that indicates the absence of a value.

<p>True (A)</p> Signup and view all the answers

The value NaN is considered equal to itself in JavaScript.

<p>False (B)</p> Signup and view all the answers

The statement '' == 0 evaluates to true in JavaScript.

<p>True (A)</p> Signup and view all the answers

In JavaScript, arrays are a subtype of objects.

<p>True (A)</p> Signup and view all the answers

The array method .pop() removes an element from the beginning of the array.

<p>False (B)</p> Signup and view all the answers

In JavaScript, using === is recommended over == for comparisons.

<p>True (A)</p> Signup and view all the answers

The length property of an array is a method that needs to be called.

<p>False (B)</p> Signup and view all the answers

A for...of loop can be used to iterate over the properties of an object.

<p>False (B)</p> Signup and view all the answers

The global object in all browsers is referred to as the document.

<p>False (B)</p> Signup and view all the answers

The expression [''] == '' evaluates to false.

<p>False (B)</p> Signup and view all the answers

Object properties in JavaScript cannot hold more than one value.

<p>False (B)</p> Signup and view all the answers

The method concat() is used to add items to the beginning of an array.

<p>False (B)</p> Signup and view all the answers

The push() method can add multiple items to an array in one call.

<p>True (A)</p> Signup and view all the answers

An undefined variable in JavaScript is one that has been declared but not initialized with a value.

<p>True (A)</p> Signup and view all the answers

The function getElementById() returns all elements with a specified id.

<p>False (B)</p> Signup and view all the answers

The addEventListener method allows you to specify an event name and a function to execute when the event occurs.

<p>True (A)</p> Signup and view all the answers

Using the defer attribute on a script tag ensures that the script is executed before the DOM is fully loaded.

<p>False (B)</p> Signup and view all the answers

The querySelector method returns all elements that match the provided CSS selector.

<p>False (B)</p> Signup and view all the answers

JavaScript allows changing the innerHTML of a DOM element directly using its ID.

<p>True (A)</p> Signup and view all the answers

The method getElementsByClassName() returns a live HTMLCollection of elements matching the specified class name.

<p>True (A)</p> Signup and view all the answers

The JavaScript DOM API makes it possible to create new HTML elements dynamically.

<p>True (A)</p> Signup and view all the answers

HTML attributes can be accessed as properties of DOM objects in JavaScript.

<p>True (A)</p> Signup and view all the answers

The script tag should always be placed at the beginning of the HTML document to ensure proper loading.

<p>False (B)</p> Signup and view all the answers

The querySelectorAll() function is used to retrieve the first matching element of a selector.

<p>False (B)</p> Signup and view all the answers

Flashcards

Function Declaration

A way to define a function using the function keyword.

Hoisting

JavaScript moves function declarations to the top of their scope before execution.

Function Scope

Variables declared with var are accessible throughout the entire function.

Block Scope

Variables declared with let or const are only accessible within their block.

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Variable Declaration with var

Variables declared with var are not block-scoped and persist after conditionals.

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Let Scope

Variables declared with let cannot be accessed outside their block, causing an error if attempted.

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Const Declaration

Variables declared with const maintain block scope and cannot be reassigned once set.

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Function Output

Refers to what is displayed in the console from console.log statements.

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for...in loop

A loop in JavaScript that iterates over object properties.

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for...of loop

A loop in JavaScript that iterates over iterable objects, like arrays.

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event-driven programming

A programming paradigm where code runs in response to events.

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event handler

A function that executes in response to an event.

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DOM

Document Object Model; the structure representing HTML elements.

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modifying the DOM

Changing, adding, or removing nodes in the DOM structure.

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object in JavaScript

A collection of key-value pairs allowing data organization.

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event

A signal that something occurred, like a mouse click.

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ECMAScript 2015 (ES6)

An update to JavaScript introducing new features like classes and arrow functions.

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Promises in JavaScript

An object that represents the eventual completion or failure of an asynchronous operation.

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Fetch API

A modern interface for making HTTP requests, replacing XMLHttpRequest.

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Let and Const

Scoping rules in JavaScript; 'let' is block-scoped, 'const' is immutable.

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Arrow Functions

A shorthand syntax for writing functions in JavaScript, denoted by '=>' .

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Dynamic Typing

Variables can hold any data type and can change type at runtime.

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Static Typing

Variables are bound to a specific type, checked at compile time.

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Weakly Typed Language

A programming language where operations can be performed on mismatched types.

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JavaScript ecosystem

A collection of libraries and frameworks built around JavaScript for development.

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JavaScript Usage

The widespread use of JavaScript, powering about 95% of websites.

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querySelector

A method to access the first matching DOM element using a CSS selector.

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getElementById

A function that selects a DOM element by its unique ID.

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addEventListener

Attaches an event listener to a DOM object to respond to events.

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event name

The specific event type to listen for, such as 'click' or 'focus'.

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defer attribute

An attribute for the script tag that delays execution until the DOM is fully loaded.

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innerHTML

Property to modify the HTML content inside a specified element.

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modifying attributes

Changing the attributes of a DOM element through JavaScript.

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getElementsByTagName

A method that returns a list of elements with a specified tag name.

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getElementsByClassName

A function that selects all DOM elements with a specified class name.

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creating DOM elements

The process of generating new elements within the DOM using JavaScript.

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const variable

A variable that cannot be reassigned but can have its content modified.

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null

A value indicating the absence of a value, like an empty variable.

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undefined

A value for variables that haven't been assigned a value yet.

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truthy values

Values that evaluate to true in a boolean context, except for falsy values.

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falsy values

Values that evaluate to false in a boolean context: null, undefined, 0, NaN, '', and false.

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== operator

Equality operator that evaluates values for equality with type coercion.

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=== operator

Strict equality operator that checks both value and type without coercion.

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arrays

Data structures that store ordered lists of elements, starting at index 0.

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push() method

Adds new items to the end of an array.

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for loop

A control structure for iterating over ranges or collections of items.

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object

A collection of key-value pairs, where keys are identifiers.

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JSON

JavaScript Object Notation, a lightweight format for data interchange.

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length property

A property of arrays that returns the number of elements it contains.

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Using HTML Element

Incorporating JavaScript code within an HTML element.

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External JavaScript File

JavaScript code stored in a separate file, linked to HTML.

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Types of Variables

Variables can be declared using var, let, or const.

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JavaScript Execution

Scripts run from top to bottom without a main method.

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JIT Compilation

JavaScript is compiled dynamically by the browser.

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Console.log()

Outputs messages to the web browser's console.

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Alert Function

Displays a pop-up message to the user.

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Document.write()

Writes content directly to the HTML document.

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While Loop

Repeats a block of code as long as a condition is true.

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Study Notes

JavaScript Overview

  • Introduction to Programming and Systems on the Web
  • Introduction to JavaScript ('vanilla' JS)
  • Basic language features
  • Event handling
  • DOM manipulation

JavaScript Details

  • Function expressions
  • Promises
  • JavaScript functional programming
  • Currying, closures, lambda functions
  • JavaScript frameworks

ECMAScript 2015 (ES6)

  • Class support
  • Iterator and for/of loops
  • Promises
  • Fetch API
  • Let, const, vs. var
  • Arrow functions (lambdas)
  • Currying function

JavaScript in use

  • Usage in web applications
  • Node.js use cases
  • Popularity of JavaScript for website development

JavaScript Frameworks and Libraries

  • 95% of web pages use JavaScript
  • Node.js, React, jQuery, React, Vue.js, Angular are popular choices

Data Types and Variables

  • Primitive types (booleans, numbers, strings, null, undefined, bigint, symbol)
  • Reference types (arrays, objects)
  • var keyword (function-level scope)
  • let keyword (block scope)
  • const keyword (block scope, immutable)
  • Hoisting behavior

DOM Manipulation

  • JavaScript interaction with HTML elements
  • Document Object Model (DOM)
  • Accessing and modifying HTML elements
  • Using query selectors
  • Manipulating attributes
  • Adding/removing elements
  • Event handling
  • Inline events
  • Event listeners

Function Declarations

  • Function definition
  • Function parameters
  • Function return value

Working with Arrays

  • Array creation
  • Array indexing (zero-based)
  • Array methods (push, pop, concat, slice, join, reverse, shift, sort)

Object Manipulation

  • Object creation
  • Accessing object properties
  • Using dot and bracket notation
  • Object methods

JavaScript's Event Handling

  • JavaScript event handling
  • Event handlers
  • Asynchronous execution
  • DOM functions

JavaScript's Console Output

  • Using alert(), console.log, and document.write

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Description

This quiz covers an extensive overview of JavaScript, including its fundamental features, event handling, and DOM manipulation. It also delves into advanced topics such as ES6 features, functional programming, and popular JavaScript frameworks used in web development. Test your knowledge on the language that powers the majority of web applications!

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