Built-in Methods - Exercises

Multiple Choice Questions

Question 1

What does Math.floor(4.7) return? A) 5 B) 4 C) 4.7 D) Error

Answer: B Explanation: Math.floor() rounds down to the nearest integer, so 4.7 becomes 4.

Question 2

Which method converts a string to an array? A) split() B) slice() C) splice() D) join()

Answer: A Explanation: The split() method splits a string into an array based on a delimiter.

Question 3

What does "hello".charAt(1) return? A) “h” B) “e” C) “l” D) “o”

Answer: B Explanation: charAt(1) returns the character at index 1, which is “e”.

Question 4

Which method returns the current date and time as a number? A) Date.now() B) Date.time() C) Date.current() D) Date.get()

Answer: A Explanation: Date.now() returns the current timestamp in milliseconds since January 1, 1970.

Question 5

What does Math.random() return? A) A random integer between 0 and 1 B) A random decimal between 0 and 1 (excluding 1) C) A random integer between 1 and 10 D) A random decimal between 1 and 10

Answer: B Explanation: Math.random() returns a random decimal number between 0 (inclusive) and 1 (exclusive).

Question 6

Which method checks if an array includes a specific element? A) contains() B) has() C) includes() D) indexOf()

Answer: C Explanation: The includes() method returns true if the array contains the specified element.

Practical Coding Exercises

Exercise 1: Math Methods Practice

Create a script that asks the user for a list of numbers and then performs several calculations using the Math object.

Instructions:

Prompt the user to enter a comma-separated list of numbers.
Use Math.max() and Math.min() to find the largest and smallest numbers.
Calculate the sum of the numbers. A for loop is a good choice here.
Generate a random integer between the min and max values.
Display the results in an alert box.

Starter Code:

function mathOperations() {
  const input = prompt(
    "Enter a list of numbers separated by commas (e.g., 1, 2, 3):",
  );
  if (!input) {
    alert("No input provided. Please try again.");
    return;
  }

  // TODO: Convert the input string into an array of numbers.
  // Hint: Use split(',') and then convert each part to a number.
  const numbers = []; // Your code here

  // TODO: Find the maximum value using Math.max().
  // Hint: The spread operator (...) is useful here.
  const max = 0; // Your code here

  // TODO: Find the minimum value using Math.min().
  const min = 0; // Your code here

  // TODO: Calculate the sum of the numbers using a for loop.
  let sum = 0;
  // Your code here

  // TODO: Generate a random number between min and max (inclusive).
  // Hint: Math.random() * (max - min + 1) + min
  const randomInRange = 0; // Your code here

  // Display the results
  const results = `
    Original Numbers: ${numbers.join(", ")}
    Maximum: ${max}
    Minimum: ${min}
    Sum: ${sum}
    Random Number in Range: ${randomInRange}
  `;

  alert(results);
}

// Run the function
mathOperations();

Solution:

function mathOperations() {
  const input = prompt(
    "Enter a list of numbers separated by commas (e.g., 1, 2, 3):",
  );
  if (!input) {
    alert("No input provided. Please try again.");
    return;
  }

  // Convert the input string into an array of numbers.
  const numbers = input.split(",").map(Number);

  // Find the maximum value
  const max = Math.max(...numbers);

  // Find the minimum value
  const min = Math.min(...numbers);

  // Calculate the sum
  let sum = 0;
  for (let i = 0; i < numbers.length; i++) {
    sum += numbers[i];
  }

  // Generate a random number between min and max (inclusive)
  const randomInRange = Math.floor(Math.random() * (max - min + 1)) + min;

  // Display the results
  const results = `
    Original Numbers: ${numbers.join(", ")}
    Maximum: ${max}
    Minimum: ${min}
    Sum: ${sum}
    Random Number in Range: ${randomInRange}
  `;

  alert(results);
}

Exercise 2: String Methods Mastery

Create a script that asks the user for a sentence and then manipulates it using various string methods.

Instructions:

Prompt the user to enter a sentence.
Perform a series of transformations: convert to uppercase, lowercase, and trim whitespace.
Replace all spaces with underscores.
Extract the first 10 characters as an excerpt.
Check if the original sentence includes the word “javascript” (case-insensitive).
Display the results in an alert box.

Starter Code:

function stringManipulation() {
  const text = prompt("Enter a sentence:");
  if (!text) {
    alert("No input provided. Please try again.");
    return;
  }

  // TODO: Convert to uppercase.
  const uppercase = ""; // Your code here

  // TODO: Convert to lowercase.
  const lowercase = ""; // Your code here

  // TODO: Remove whitespace from beginning and end.
  const trimmed = ""; // Your code here

  // TODO: Replace all spaces with underscores.
  // Hint: Use the replaceAll() method.
  const withUnderscores = ""; // Your code here

  // TODO: Extract the first 10 characters.
  // Hint: Use substring() or slice().
  const excerpt = ""; // Your code here

  // TODO: Check if it contains "javascript" (case-insensitive).
  // Hint: Convert the text to lowercase first.
  const containsJavaScript = false; // Your code here

  const results = `
    Original: "${text}"
    Uppercase: ${uppercase}
    Lowercase: ${lowercase}
    Trimmed: "${trimmed}"
    With Underscores: ${withUnderscores}
    Excerpt: "${excerpt}..."
    Contains "JavaScript"?: ${containsJavaScript ? "Yes" : "No"}
  `;

  alert(results);
}

// Run the function
stringManipulation();

Solution:

function stringManipulation() {
  const text = prompt("Enter a sentence:");
  if (!text) {
    alert("No input provided. Please try again.");
    return;
  }

  // Convert to uppercase
  const uppercase = text.toUpperCase();

  // Convert to lowercase
  const lowercase = text.toLowerCase();

  // Remove whitespace from beginning and end
  const trimmed = text.trim();

  // Replace all spaces with underscores
  const withUnderscores = trimmed.replaceAll(" ", "_");

  // Extract first 10 characters
  const excerpt = text.substring(0, 10);

  // Check if it contains a specific substring (case-insensitive)
  const containsJavaScript = text.toLowerCase().includes("javascript");

  const results = `
    Original: "${text}"
    Uppercase: ${uppercase}
    Lowercase: ${lowercase}
    Trimmed: "${trimmed}"
    With Underscores: ${withUnderscores}
    Excerpt: "${excerpt}..."
    Contains "JavaScript"?: ${containsJavaScript ? "Yes" : "No"}
  `;

  alert(results);
}

Exercise 3: Date Methods Practice

Create a script that displays information about the current date and calculates the days until the new year.

Instructions:

Create a new Date() object for the current moment.
Get the current year, month, and day.
Create a Date object for the first day of the next year.
Calculate the difference in days between today and New Year’s Day.
Format today’s date into a readable string (e.g., “December 25, 2023”).
Display all the collected information in an alert box.

Starter Code:

function dateOperations() {
  // TODO: Create a new date for today.
  const today = null; // Your code here

  // TODO: Get the current year.
  const currentYear = 0; // Your code here

  // TODO: Get the current month (0-11).
  const currentMonthIndex = 0; // Your code here

  // TODO: Get the current day of the month.
  const currentDay = 0; // Your code here

  // TODO: Create a date for the first day of the next year.
  const nextYear = currentYear + 1;
  const newYearDate = null; // Your code here

  // TODO: Calculate the difference in milliseconds between now and New Year's.
  const timeDiff = 0; // Your code here

  // TODO: Convert the time difference to days.
  // Hint: 1000ms * 60s * 60min * 24hr
  const daysUntilNewYear = 0; // Your code here

  // TODO: Format today's date as a readable string.
  // Example: "December 25, 2023"
  const formattedDate = ""; // Your code here

  const results = `
    Today's Date: ${formattedDate}
    Current Year: ${currentYear}
    Days Until New Year: ${daysUntilNewYear}
  `;

  alert(results);
}

// Run the function
dateOperations();

Solution:

function dateOperations() {
  // Create a new date for today
  const today = new Date();

  // Get the current year
  const currentYear = today.getFullYear();

  // Get the current month (0-11)
  const currentMonthIndex = today.getMonth();

  // Get the current day of month
  const currentDay = today.getDate();

  // Create a date for the first day of the next year
  const newYearDate = new Date(currentYear + 1, 0, 1);

  // Calculate days until the new year
  const timeDiff = newYearDate.getTime() - today.getTime();
  const daysUntilNewYear = Math.ceil(timeDiff / (1000 * 3600 * 24));

  // Format today as a readable string
  const months = [
    "January",
    "February",
    "March",
    "April",
    "May",
    "June",
    "July",
    "August",
    "September",
    "October",
    "November",
    "December",
  ];
  const formattedDate = `${months[currentMonthIndex]} ${currentDay}, ${currentYear}`;

  const results = `
    Today's Date: ${formattedDate}
    Current Year: ${currentYear}
    Days Until New Year: ${daysUntilNewYear}
  `;

  alert(results);
}

Exercise 4: JSON and Object Methods

Create a script that works with a JSON string representing user data.

Instructions:

Start with a given JSON string.
Use JSON.parse() to convert the string into a JavaScript object.
Use Object.keys(), Object.values(), and Object.entries() to inspect the object’s properties.
Use JSON.stringify() to convert the object back into a formatted JSON string.
Display the results in an alert box.

Starter Code:

function jsonOperations() {
  const userDataString =
    '{"name": "Alice", "age": 30, "hobbies": ["reading", "coding"], "isActive": true}';

  // TODO: Parse the JSON string into an object.
  const userData = {}; // Your code here

  // TODO: Get all property keys from the object.
  const keys = []; // Your code here

  // TODO: Get all property values.
  const values = []; // Your code here

  // TODO: Get key-value pairs as an array of arrays.
  const entries = []; // Your code here

  // TODO: Convert the object back to a JSON string (with formatting).
  // Hint: Use the third argument of JSON.stringify for indentation.
  const formattedJson = ""; // Your code here

  const results = `
    Original JSON String:
    ${userDataString}

    Object Keys:
    ${keys.join(", ")}

    Object Values:
    ${values.join(" | ")}

    Formatted JSON:
    ${formattedJson}
  `;

  alert(results);
  console.log("Key-Value Entries:", entries);
}

// Run the function
jsonOperations();

Solution:

function jsonOperations() {
  const userDataString =
    '{"name": "Alice", "age": 30, "hobbies": ["reading", "coding"], "isActive": true}';

  // Parse the JSON string
  const userData = JSON.parse(userDataString);

  // Get all property keys
  const keys = Object.keys(userData);

  // Get all property values
  const values = Object.values(userData);

  // Get key-value pairs as arrays
  const entries = Object.entries(userData);

  // Convert object back to JSON string (with formatting)
  const formattedJson = JSON.stringify(userData, null, 2);

  const results = `
    Original JSON String:
    ${userDataString}

    Object Keys:
    ${keys.join(", ")}

    Object Values:
    ${values.join(" | ")}

    Formatted JSON:
    ${formattedJson}
  `;

  alert(results);
  console.log("Key-Value Entries:", entries);
}