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Questions and Answers
What is the purpose of single line comments in JavaScript?
What is the purpose of single line comments in JavaScript?
Which statement correctly describes the multi-line comment structure in JavaScript?
Which statement correctly describes the multi-line comment structure in JavaScript?
How can you prevent the execution of a specific line of code using comments?
How can you prevent the execution of a specific line of code using comments?
What will happen if a multi-line comment is used to comment out a block of code?
What will happen if a multi-line comment is used to comment out a block of code?
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Which of the following is a valid use of comments in JavaScript?
Which of the following is a valid use of comments in JavaScript?
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What is indicated by placing a comment at the end of a line of code?
What is indicated by placing a comment at the end of a line of code?
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Which of the following best describes the primary use of comments in debugging?
Which of the following best describes the primary use of comments in debugging?
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What indicates a problem in the code within a comment when debugging?
What indicates a problem in the code within a comment when debugging?
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What is the primary purpose of JavaScript functions?
What is the primary purpose of JavaScript functions?
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Which of the following correctly defines a JavaScript function?
Which of the following correctly defines a JavaScript function?
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How can you call a function in JavaScript?
How can you call a function in JavaScript?
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What will be the output of the following code: function add(a, b) { return a + b; } alert(add(2, 3));?
What will be the output of the following code: function add(a, b) { return a + b; } alert(add(2, 3));?
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Which term describes a function that calls itself?
Which term describes a function that calls itself?
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What does the 'return' statement do in a JavaScript function?
What does the 'return' statement do in a JavaScript function?
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Which of the following is NOT a valid way to declare a function in JavaScript?
Which of the following is NOT a valid way to declare a function in JavaScript?
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What is the effect of declaring a function inside another function?
What is the effect of declaring a function inside another function?
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What is the primary purpose of a function in JavaScript?
What is the primary purpose of a function in JavaScript?
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How do you define a function in JavaScript?
How do you define a function in JavaScript?
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What keyword is used to call a JavaScript function?
What keyword is used to call a JavaScript function?
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What can a JavaScript function return?
What can a JavaScript function return?
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What will happen if a function is called without any parameters?
What will happen if a function is called without any parameters?
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Which of the following is a valid way to assign a function to a variable?
Which of the following is a valid way to assign a function to a variable?
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In JavaScript, what are parameters used for in functions?
In JavaScript, what are parameters used for in functions?
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What is the result of executing a function that does not explicitly return a value?
What is the result of executing a function that does not explicitly return a value?
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Study Notes
JavaScript Overview
- JavaScript is the scripting language of the web
- Used in millions of web pages to add functionality
- Used for form validation, browser detection, and much more
JavaScript Statements
- Sequences of instructions executed in order
- Semicolons are optional, though recommended
- Single-line comments use //
- Multi-line comments use /* */
JavaScript Variables
- Containers to store data
- Case-sensitive
- Must start with a letter or underscore
- Can be declared with 'var'
JavaScript Operators
- Used to perform calculations
- Arithmetic operators (+, -, *, /, %, ++, --)
- Assignment operators (=, +=, -=, *=, /=, %=)
JavaScript Comparisons and Logical Operators
- Comparison operators (==, ===, !=, >, <, >=, <=) used to compare values
- Logical operators (&&, ||, !) used to combine or negate conditions
JavaScript If...Else Statements
- Conditional statements to perform different actions based on conditions
- 'if' statement for executing code if a condition is true
- 'if...else' statement for executing different code if a condition is false
- 'if...else if...else' statement for selecting among multiple conditions
- 'switch' statement for selecting among multiple blocks based on conditions
JavaScript Popup Boxes
- Alert, Confirm, and Prompt boxes to interact with users
- Alert displays a message
- Confirm displays a message, accepting or canceling
- Prompt lets users enter values
JavaScript Functions
- Reusable blocks of code
- Defined using 'function' keyword, followed by a name parentheses containing parameters, and curly braces containing code
- Execute when called by name
- Return values using 'return'
JavaScript Loops
- 'for' loop executes a block of code a predetermined number of times
- 'while' loop executes a block of code as long as a condition is true
- 'do...while' loop executes a block of code at least once, then repeatedly as long as a condition is true
JavaScript Break and Continue Statements
- 'break' statement exits a loop prematurely
- 'continue' statement skips the rest of the current loop iteration and proceeds to the next.
JavaScript For...In Statement
- Used to loop through elements in an array or through properties of an object
JavaScript Events
- Actions that trigger JavaScript code execution
- 'onload' or 'onunload': for page load or leaving the page respectively
- 'onfocus', 'onblur', or 'onchange': for field focus/blur/change respectively
- Event listeners can prevent or change default behaviors
JavaScript Try...Catch Statement
- Used for handling errors in code
- 'try' block contains code that might cause errors
- 'catch' block handles errors that occur in the 'try' block.
JavaScript Throw Statement
- Used to manually create an error to handle in try/catch blocks.
JavaScript Special Characters
- Use backslash () to insert special characters into strings (e.g., ' for an apostrophe, " for a double quote, \n for a new line) .
JavaScript Guidelines
- Case-sensitivity: JavaScript is case-sensitive (e.g., myFunction is different from Myfunction).
- White space: Extra spaces are ignored.
- Code lines: Break up long lines with backslashes for readability but not between functions.
JavaScript Objects
- Collections of properties and methods
- Create objects using the constructor function approach
JavaScript Number Object
- Wrapper object around primitive number values
- Methods used include but are not limited to
- toFixed(x): Formats a number with x digits after the decimal point
- toExponential(x): Formats a number in exponential notation.
JavaScript String Object
- Manages text strings and gives functions to manipulate them.
- Methods include but are not limited to
- charAt(x) returns the character at index x,
- toUpperCase(): converts to uppercase letters.
JavaScript Date Object
- Represents dates and times
- Methods include but are not limited to: setTime() to set times, getFullYear() to get the year, setDate() to set the date.
JavaScript Array Object
- Stores multiple values in a single variable
- Methods include but are not limited to: push() to add elements to the end of an array, pop() to remove an element from the end.
JavaScript Boolean Object
- Used to represent true/false values
- Methods include but are not limited to: toString() to convert a Boolean to a string,
JavaScript Math Object
- Provides mathematical functions
JavaScript RegExp Object
- Used for complex pattern matching
- Has methods like test() (returns true if the pattern matches) and exec() (returns the first match).
JavaScript Browser Detection
- Using the Navigator object, extract useful string information about the user's browser.
JavaScript Cookies
- Used to store information on the visitor's computer; accessed through the document.cookie object
- Methods include setCookie() to create and store and getCookie() to retrieve cookies.
JavaScript Form Validation
- Used to check user input for correctness before submitting a form
- Common checks include validating required fields, email addresses, and dates.
JavaScript Animation
- Modifying the src of images to create animation
JavaScript Image Maps
- Working with clickable regions within images.
JavaScript Timing Events
- Uses setTimeout() for timed execution of code
- clearTimeout() used to cancel a delayed action.
JavaScript HTML DOM Objects
- Used to access and interact with HTML elements programmatically
- Methods and properties to manipulate elements, access attributes, manage events, etc.
JavaScript Global Properties
- Infinity, NaN, undefined
JavaScript Global Functions
- Functions including decodeURI, encodeURI, escape, eval, isFinite, isNaN.
JavaScript Objects - Advanced
- Methods to create custom objects, adding properties and functions to them dynamically.
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Description
Test your knowledge on the use of comments and functions in JavaScript with this quiz. Covering single and multi-line comments, function calling, and debugging, you'll get a comprehensive understanding of these essential programming concepts. See how well you know JavaScript's syntax and functionality!
