In this lab, you will explore how JavaScript stores and manipulates data using:

• Strings (text)
• Numbers (math)
• Arrays (lists)
• Objects (structured data)

This is a guided walkthrough lab, meaning:

• You will read → try → build → reflect
• Each section builds on the previous one
• You will combine everything at the end

By the end of this lab, you will be able to:

• Manipulate strings using built-in methods
• Perform mathematical operations with numbers
• Store and loop through data using arrays
• Create and access objects with key-value pairs
• Combine all concepts into real-world scenarios

mkdir js-data-types-lab
cd js-data-types-lab
touch lab.js
code .
node lab.js

js-data-types-lab/
│
└── lab.js

A string is text wrapped in quotes.

let name = "Coreye";

let message = "hello world";

message.length        // length of string
message.toUpperCase() // HELLO WORLD
message.toLowerCase() // hello world
message.includes("world") // true
message.slice(0, 5)   // hello

Create a variable:

let fullName = "your name here";

• Print the length of the string
• Convert it to uppercase
• Check if it includes your last name
• Slice out your first name only

Create a function that:

• Accepts a name
• Returns: "Hello, NAME!" (all caps)

1. What does .length do?
2. What does .includes() return?
3. What does .slice() do?

A number represents numeric values.

let age = 25;
let price = 19.99;

let a = 10;
let b = 3;

a + b  // addition
a - b  // subtraction
a * b  // multiplication
a / b  // division
a % b  // remainder

Math.round(4.6) // 5
Math.floor(4.9) // 4
Math.ceil(4.1)  // 5
Math.random()   // random number 0–1

Create variables:

let num1 = 10;
let num2 = 3;

• Add, subtract, multiply, divide
• Find remainder
• Round a decimal number
• Generate a random number between 1–10

Create a function that:

• Accepts a number

• Returns:

  • "Even" if even
  • "Odd" if odd

1. What does % do?
2. What does Math.random() return?
3. When would you use Math.floor()?

An array is a list of values.

let fruits = ["apple", "banana", "orange"];

fruits[0] // apple
fruits[1] // banana

fruits.push("grape")   // add to end
fruits.pop()           // remove last
fruits.length          // number of items

for (let i = 0; i < fruits.length; i++) {
  console.log(fruits[i]);
}

Create an array:

let students = ["A", "B", "C", "D"];

• Print all students
• Add a new student
• Remove the last student
• Print total number of students

Create a function that:

• Accepts an array of numbers
• Returns the sum of all numbers

1. How do you access an array element?
2. What does .push() do?
3. Why do we use loops with arrays?

An object stores data as key-value pairs.

let person = {
  name: "Coreye",
  age: 25,
  isStudent: true
};

person.name
person["age"]

person.age = 26;

for (let key in person) {
  console.log(key, person[key]);
}

Create an object:

let car = {
  brand: "Toyota",
  model: "Camry",
  year: 2020
};

• Print each property
• Update the year
• Add a new property (color)
• Loop through the object

Create a function that:

• Accepts a person object
• Returns a sentence like: "Name is AGE years old"

1. What is a key-value pair?
2. How do you access object data?
3. When would you use an object instead of an array?

Create:

A student object:

{
  name: "Student Name",
  scores: [80, 90, 75, 100]
}

Build a program that:

• Loops through scores

• Calculates average

• Determines grade:

  • A, B, C, D, F

• Prints:

Name: John
Average: 86
Grade: B

• Must use:

  • arrays (scores)
  • object (student)
  • loop (iterate scores)
  • function (calculate average)
  • conditionals (grade logic)

• ✅ Completed lab.js
• ✅ All 4 sections completed
• ✅ Mini challenges completed
• ✅ Final challenge completed
• ✅ Reflection questions

At the bottom of your file, answer:

1. Which data type felt easiest?
2. Which one was most confusing?
3. How do arrays and objects differ?
4. When would you use each in real applications?

• Test everything with console.log()
• Break problems into steps
• Don’t try to do everything at once
• If stuck → simplify