JavaScript Basics Overview
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Questions and Answers

Which of the following statements about the 'const' keyword in JavaScript are true?

  • It declares variables that cannot be reassigned. (correct)
  • It was introduced in ECMAScript2015. (correct)
  • It declares variables that are always scoped globally.
  • It declares variables that can be redeclared within the same scope.

    • Which statement correctly describes the impact of declaring a variable with the 'var' keyword inside a function?

  • The variable is scoped to the block in which it's declared and can only be accessed within that block.
  • The variable's scope is determined by the closest enclosing block.
  • The variable is scoped to that specific function and cannot be accessed from outside. (correct)
  • The variable becomes global and can be accessed anywhere in the program.

    • Why is it recommended to avoid using the 'var' keyword as much as possible?

  • 'var' variables are less efficient than variables declared with 'let' and 'const'.
  • 'var' variables can cause unexpected behavior when used with nested functions.
  • 'var' variables are deprecated and no longer supported in modern JavaScript.
  • 'var' variables can easily lead to unintended side effects because they are always globally scoped. (correct)

    • Which of the following data types is NOT a primitive data type in JavaScript?

    <p>Object (C)</p> Signup and view all the answers

    What is the primary difference between the 'let' and 'const' keywords?

    <p>'let' variables can be reassigned, while 'const' variables cannot. (C)</p> Signup and view all the answers

    Which static property represents the largest possible positive number in JavaScript?

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

    Which JavaScript function rounds a number down to the nearest integer?

    <p>Math.floor() (A)</p> Signup and view all the answers

    Which operator is used for string concatenation in JavaScript?

    <ul> <li>(B)</li> </ul> Signup and view all the answers

    What does the toFixed(2) function do to a number?

    <p>Rounds the number to two decimal places (B)</p> Signup and view all the answers

    Which operation is used to find the remainder after integer division in JavaScript?

    <p>% (C)</p> Signup and view all the answers

    What is the data type of the result returned by Math.random()?

    <p>Number (C)</p> Signup and view all the answers

    In the expression condition ? value1 : value2, what does the colon (:) represent?

    <p>The ternary operator's separation between expressions (B)</p> Signup and view all the answers

    What is the result of 10 % 3?

    <p>1 (A)</p> Signup and view all the answers

    What does the filter method do in JavaScript?

    <p>It creates a new array with all elements that pass a boolean test. (C)</p> Signup and view all the answers

    Which method would you use to test if all elements in an array pass a given test?

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

    What is the result when the method some is applied to the array [3, 5, 8] with a function that checks if a number is greater than or equal to 10?

    <p>false (D)</p> Signup and view all the answers

    How does JavaScript handle object creation?

    <p>By cloning existing objects. (D)</p> Signup and view all the answers

    What does the reduceRight method do?

    <p>It reduces the array to a single value from right to left. (C)</p> Signup and view all the answers

    Which method would NOT be used to filter or reduce an array?

    <p>map (D)</p> Signup and view all the answers

    If you apply the map method to the array [1, 4, 9] using Math.sqrt, what will be the resulting array?

    <p>[1, 2, 3] (C)</p> Signup and view all the answers

    What is a characteristic of properties in JavaScript objects?

    <p>They can be dynamically added or modified. (C)</p> Signup and view all the answers

    In JavaScript, how can a function defined within an object be described?

    <p>As a method. (B)</p> Signup and view all the answers

    What does the \t escape sequence represent in a JavaScript string?

    <p>A horizontal tab (D)</p> Signup and view all the answers

    Which statement accurately describes JavaScript's type system?

    <p>JavaScript has a dynamic type system where variables are not declared with explicit types, and their types can change over time. (C)</p> Signup and view all the answers

    What is the primary purpose of wrapping objects like Number, String, and Boolean in JavaScript?

    <p>To provide methods and properties for manipulating primitive types. (D)</p> Signup and view all the answers

    Which of the following statements correctly demonstrates the concatenation of strings in JavaScript?

    <p><code>&quot;string1&quot; + &quot;string2&quot;</code> (B)</p> Signup and view all the answers

    Given var str = "abc"; and var secondLetter = str.charAt(1);, what is the value of secondLetter?

    <p>&quot;b&quot; (D)</p> Signup and view all the answers

    Which of these is a valid JavaScript string literal?

    <p>&quot;This &quot;string&quot; is valid&quot; (B), &quot;This string is valid&quot; (C), 'This string is valid' (D)</p> Signup and view all the answers

    What is the result of the expression "9" + 3 in JavaScript?

    <p>&quot;93&quot; (D)</p> Signup and view all the answers

    Flashcards

    Strict Mode

    A JavaScript feature that enforces stricter parsing and error handling.

    var, let, and const

    Keywords for declaring variables in JavaScript with different scopes and reassignability.

    Variable Scope

    Defines the accessibility of variables; either global (outside block) or local (inside block).

    Primitive Data Types

    Basic data types in JavaScript, including strings and numbers.

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    String in JavaScript

    A sequence of characters, with no separate character type.

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    Boolean

    A data type that can be either true or false.

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    Composite types

    Data types that can hold multiple values or properties, like objects and arrays.

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    Dynamic type system

    A feature where variable types are not declared and can change at runtime.

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    Automatic type conversion

    The process where JavaScript converts types automatically during operations.

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    Explicit type conversion

    Forcing a value to a specific type using conversion functions.

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    Strings

    Sequences of characters used to represent text in JavaScript.

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    Escape characters

    Special characters used to represent certain characters in strings.

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    MAX_VALUE

    The largest positive number in JavaScript.

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    MIN_VALUE

    The smallest positive number that can be represented.

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    NEGATIVE_INFINITY

    Represents the value of negative infinity in JavaScript.

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    POSITIVE_INFINITY

    Represents the value of positive infinity in JavaScript.

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    toString()

    Converts a number to its string representation.

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    toFixed()

    Returns a number with a specified number of digits after the decimal.

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    Math.pow()

    Calculates base raised to the exponent's power.

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    Math.round()

    Rounds a number to the nearest integer.

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    Comparison operators

    Operators used to compare two values.

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    some

    Tests if any element in an array passes a provided function's test.

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    filter

    Creates a new array with elements that pass a test implemented by a provided function.

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    reduce

    Applies a function against an accumulator and each array value (left-to-right) to reduce to a single value.

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    reduceRight

    Applies a function against an accumulator and each array value (right-to-left) to reduce to a single value.

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    sort

    Sorts the elements of an array using a compare function.

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    callback function

    A function passed into another function as an argument, executed at a later time.

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    objects

    Collections of properties in JavaScript, with no concept of classes.

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    prototype-based inheritance

    JavaScript objects inherit properties from other objects through a prototype chain.

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    dynamic properties

    Object properties that can be added, modified or removed at runtime.

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    Study Notes

    JavaScript - Base

    • JavaScript is the ubiquitous language for web client development
    • It's used directly or indirectly, as other languages often extend or compile to it.
    • Other languages, like CoffeeScript, Dart, and TypeScript, use JavaScript
    • WebAssembly (wasm) is an alternative but its success is yet uncertain.
    • It's a low-level bytecode format for in-browser client-side programming, suitable for web compilation.
    • JavaScript is also used on server-side platforms, such as Node.js and in various domains like game engines, spreadsheets, or IoT systems.

    Summary

    • The presentation covers JavaScript's introduction, history, data types, syntax, loops, arrays, objects, functions and many other elements
    • Key JavaScript standards include ECMA
    • The history of JavaScript editions from 1995-2024 is documented
    • Different JavaScript engines associated with browsers, such as V8 (Chrome/Opera), SpiderMonkey (Firefox), Chakra, and JavaScriptCore, are mentioned
    • Core Language characteristics like syntax basis, interpreted language, dynamic language, loosely typed, and its multi-paradigm features are highlighted

    1. Introduction and History

    • JavaScript was introduced in 1995 in Netscape Navigator 2.0 with the name Mocha
    • Later, Netscape submitted it for standardization to ECMA
    • A standard for ECMAScript (JavaScript) language called ECMAScript-262 was subsequently created
    • JavaScript versions, from the 1st to the 15th edition, were highlighted through history
    • The evolution through different editions is a key feature of the history

    2. Basic Syntax and Semantic

    • JavaScript is case-sensitive
    • Comments use // for single-line and /* */ for multi-line
    • Unicode is utilized, including escape sequences
    • Semicolons are optional, but their use is recommended

    3. Data Types

    • Primitive types include String, Number, Boolean, Null, and Undefined
    • Composite types comprise Objects, Arrays, Functions, Dates and RegExps
    • Numbers in JavaScript are handled as floating-point values
    • JavaScript has a dynamic typing system; variable types can change at runtime
    • Special values and functions for handling conversions
    • Wrapping objects (e.g., Number, String) are explained. These wrap primitives and add functions like .length
    • String literals may use single or double quotes but not both in one string, including escape characters

    4. Loop and Control Statements

    • Control, if, else; and loop statements (while, do-while, for, for...in, switch, and try...catch) are covered, illustrating syntax and providing examples.
    • Syntax is similar to C, C++, and Java.

    5. Arrays

    • JavaScript arrays can hold various data types (numbers, strings, booleans, objects).
    • Arrays are zero-indexed. The first element is at index 0
    • Arrays support standard loop through numeric indices and for-in loops
    • Several array functions (e.g. forEach,map, filter,every,some, reduce, splice)
    • Array operations like .push, .unshift, pop, .shift, .splice, .slice and .length are discussed with examples

    6. Objects

    • JavaScript is object-based, not class-based.
    • Objects are collections of key-value properties.
    • Properties can be functions (methods)
    • Objects are created through literals or by using constructors; for-in loop can be used to iterate over object properties.
    • Object.create can be utilized to create objects by cloning or extending prototypes
    • Object properties, methods of access (obj.property, obj["property"])

    7. Functions

    • JavaScript functions are objects
    • They support first-class functions (assigning, passing, returning functions as arguments)
    • Defining functions by declaration or using anonymous functions with examples.
    • Parameters mismatch cases (less or more parameters than expected).
    • Accessing parameters via arguments object

    8. Best Practices

    • Use strict mode, particularly with JavaScript code to enhance performance and prevent potential errors.
    • Adherence to coding style conventions, such as using camelCase for variables, using capital initial letters for constructors, and upper case for constants is essential, especially for maintainability and readability.
    • Use linters (e.g., JSLint) or equivalent tools to ensure code quality, identify syntax errors, and follow coding style rules.

    Bibliography

    • A section listing the sources for the JavaScript presentation materials. The bibliography includes links to useful resources.

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    JavaScript Base PDF

    Description

    This quiz covers the fundamentals of JavaScript, including its introduction, history, data types, syntax, and core features. It also discusses JavaScript's role in web development and its relationship with other languages like TypeScript and Dart. Test your knowledge of the JavaScript language and its various applications.

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