JavaScript Variables and Data Types Worksheet
Question 1
Find a reference that lists all the keywords in the JavaScript programming language.
You can explore a detailed list of JavaScript keywords on the MDN Web Docs.
Question 2
True or false: keywords and variable names are NOT case sensitive.
False. Keywords and variable names in JavaScript are case sensitive. For example, let myVariable and let MyVariable would be treated as two distinct identifiers.
Question 3
There are some rules for how you can name variables in JavaScript. What are they?
Variable names must start with a letter, _, or $.
They can only include letters, numbers, _, or $.
Names are case-sensitive.
Reserved keywords cannot be used.
Question 4
What is 'camelCase'?
CamelCase is a naming convention in programming where the first word starts with a lowercase letter, and each subsequent word starts with an uppercase letter, with no spaces between words.
Question 5
What are ALL the different data types in JavaScript (note that there are some that we did not discuss in class)?
1. String
2. Number
3. BigInt
4. Boolean
5. Undefined
6. Null
7. Symbol
8. Object
Question 6
What is a boolean data type?
A boolean data type represents one of two possible values: true or false.
It's commonly used in conditions and logical operations to make decisions in a program.
Question 7
What happens if you forget to put quotes around a string when you initialize a variable to a string value?
How does JavaScript try to interpret this?
For example: var lastName = Jones;
If you forget to put quotes around a string, JavaScript will try to interpret the value as a variable or identifier instead of a string.
In your example: var lastName = Jones;
JavaScript will assume Jones is the name of a previously declared variable. If Jones has not been declared, you will get a ReferenceError because JavaScript cannot find a variable named Jones.
To correctly assign a string value, you need to use quotes like this: var lastName = "Jones";
Question 8
What character is used to end a statement in JavaScript?
The semicolon (;) is used to end a statement in JavaScript.
For example:let name = "Alice";
console.log(name);
Question 9
If you declare a variable, but do not initialize it, what value will the variable store?
If you declare a variable but do not initialize it, the variable will store the value undefined in JavaScript.
For example:
let myVariable;
console.log(myVariable); // Output: undefined
This indicates that the variable exists but has not been assigned any value yet.
Question 10
What output will the following program produce?
In other words, explain what you would see in the console log
if you ran a program like this:
const firstTestScore = 98;
const secondTestScore = "88";
const sum = firstTestScore + secondTestScore;
console.log(sum);
console.log(typeof sum);
Here's what would happen when you run the program:
const sum = firstTestScore + secondTestScore;: Since firstTestScore is a number (98) and secondTestScore is a string ("88"), JavaScript will perform string concatenation instead of arithmetic addition. This is because when a number and a string are combined using +, the number is converted to a string. As a result, sum becomes "988" (a string).
console.log(sum);: This will output "988" to the console.
console.log(typeof sum);: The typeof operator will return "string" because the value of sum is a string.
Output in the console:
988
string
Question 11
What output will the following program produce?
In other words, explain what you would see in the console log
if you ran a program like this:
const total = 99;
console.log("total");
console.log(total);
Here's what the program will produce:
console.log("total");: This will print the string "total" to the console, because it's enclosed in quotes, indicating it's a literal string.
console.log(total);: This will print the value of the variable total, which is 99.
Output in the console:
total
99
Question 12
What is the difference between these two variables?
const score1 = 75;
const score2 = "75";
The difference lies in the data types of the two variables:
score1 is a number (a numerical value).
score2 is a string (text surrounded by quotes).
This means they are stored and treated differently in JavaScript. For example:
console.log(score1 + score1); // Output: 150 (addition of numbers)
console.log(score2 + score2); // Output: "7575" (concatenation of strings)
Question 13
Explain why the this code will cause the program to crash:
const score = 0;
score = prompt("Enter a score");
This code will cause the program to crash because you're attempting to reassign a value to a constant variable. In JavaScript, variables declared with const cannot have their value changed after they are initialized. In the code:
const score = 0;
score = prompt("Enter a score");
The first line creates a constant variable score with an initial value of 0. On the second line, you attempt to reassign a new value to score using the prompt function. This will throw a TypeError, as constants cannot be reassigned.
To fix this, you can use the let keyword instead of const if the value of score needs to be updated:
let score = 0;
score = prompt("Enter a score");
Coding Problems
Coding Problems - See the 'script' element below this h1 element. You will have to write some JavaScript code in it.
Here are some tips to help you with the coding problems:
- To do this assignment, you'll need to know how to open the brower's developer tools (press F12) and look at the console log.
- Pay extremely close attention to syntax! One little syntax error can mess up your entire program.
- After you complete each problem, refresh the page in the browser and look in the console your log message and for errors.
- If you have an error in the console, check the line number of the error then look for syntax errors on that line (and the line before and the line after that line).
-
If you get stuck on this assignment, please ask for help!
Dealing with syntax errors can be extremely frustrating for beginners. It takes a lot
of effort and support to get comfortable with the syntax of a language. Don't be afraid to ask for help, your success
in this class will depend on your willingness to get help!