JavaScript Review

Question 1

There are two functions being called in the code sample below. Which one returns a value? How can you tell? 

let grade = calculateLetterGrade(96);
submitFinalGrade(grade);
The function calculateLetterGrade returns the value because it is assigned to grade.
Question 2

Explain the difference between a local variable and a global variable.

A local variable is a variable declared inside a function or block. A global variable is declared outside of any function and can be accessed from anywhere in the program.
Question 3

Which variables in the code sample below are local, and which ones are global? 

const stateTaxRate = 0.06;
const federalTaxRate = 0.11;

function calculateTaxes(wages){
	const totalStateTaxes = wages * stateTaxRate;
	const totalFederalTaxes = wages * federalTaxRate;
	const totalTaxes = totalStateTaxes + totalFederalTaxes;
	return totalTaxes;
}
The global variables are stateTaxRate and federalTaxRate.

The local variables are wages, totalStateTaxes, totalFederalTaxes, and totalTaxes.

Question 4

What is the problem with this code (hint: this program will crash, explain why): 

function addTwoNumbers(num1, num2){
	const sum = num1 + num2;
	alert(sum);
}

alert("The sum is " + sum);
addTwoNumbers(3,7);
Sum isn't declared globally only locally so you would have to write

let sum; to declare it globally.

Question 5

True or false - All user input defaults to being a string, even if the user enters a number.

True (by default) .
Question 6

What function would you use to convert a string to an integer number?

parseInt().
Question 7

What function would you use to convert a string to a number that has a decimal in it (a 'float')?

parseFloat().
Question 8

What is the problem with this code sample: 

let firstName = prompt("Enter your first name");
if(firstName = "Bob"){
	alert("Hello Bob! That's a common first name!");
}
The if line needs to have double equal signs to comapre it because a single equal sign is assigning firstname to Bob.

Corect line: if(firstName == "Bob")

Question 9

What will the value of x be after the following code executes (in other words, what will appear in the log when the last line executes)? 

let x = 7;
x--;
x += 3;
x++;
x *= 2;
console.log(x);
20.
Question 10

Explain the difference between stepping over and stepping into a line of code when using the debugger.

Step vover - You don’t need to debug inside a function, just move past it.

Step into - You want to debug inside the function being called.

Coding Problems

Coding Problems - See the 'script' tag at the bottom of the page. You will have to write some JavaScript code in it.