Home HTML Data Types DOM JavaScript JS Debugging

College Board Big Idea 1

Identifying and Correcting Errors (Unit 1.4)

Become familiar with types of errors and strategies for fixing them

  • Review CollegeBoard videos and take notes on blog
  • Complete assigned MCQ questions if applicable

Code Segments

Practice fixing the following code segments!

Segment 1: Alphabet List

Intended behavior: create a list of characters from the string contained in the variable alphabet

Code:

tox: true comments: true layout: post title: JS error description: An introduction to key topics in Web Programming type: hacks courses: {compsci: {week: 6} } —

%%js

var alphabet = "abcdefghijklmnopqrstuvwxyz";
var alphabetList = [];

for (var i = 0; i < 26; i++) {
	alphabetList.push(alphabet[i]);
}

console.log(alphabetList);

<IPython.core.display.Javascript object>

What I Changed

I replaced alphabetList.push(i) into alphabetList.push(alphabet[i]) because before the code wasn’t reading the variable alphabet so it displayed numbers instead of the letters. I changed the i < 10 to 26 to get the whole alphabet.

Segment 2: Numbered Alphabet

Intended behavior: print the number of a given alphabet letter within the alphabet. For example:

"_" is letter number _ in the alphabet

Where the underscores (_) are replaced with the letter and the position of that letter within the alphabet (e.g. a=1, b=2, etc.)

Code:

%%js

// Copy your previous code to built alphabetList here
var alphabet = "abcdefghijklmnopqrstuvwxyz";
var alphabetList = [];

for (var i = 0; i < 10; i++) {
	alphabetList.push(alphabet[i]);
}

console.log(alphabetList);

let letterNumber = 5;

for (var i = 0; i < alphabetList.length; i++) {
	if (i === letterNumber-1) {
		console.log(alphabetList[letterNumber-1] + " is letter number " + letterNumber + " in the alphabet ");
	}
}

// Should output:
// "e" is letter number 5 in the alphabet

<IPython.core.display.Javascript object>

What I Changed

I included the code from the previous assignment. Then I changed for (var i = 0; i < alphabetList; i++) into for (var i = 0; i < alphabetList.length; i++) and then changed i===letterNumber into i===letterNumber-1 because it was printing f before. Then I changed console.log(letterNumber + “ is letter number 1 in the alphabet “); into console.log(alphabetList[letterNumber-1] + “ is letter number “ + letterNumber + “ in the alphabet “); because before it would only show numbers because of not being presented in the alphabet.

Segment 3: Odd Numbers

Intended behavior: print a list of all the odd numbers below 10

Code:

%%js

let odds = [];
let i = 1;

while (i < 10) {
  odds.push(i);
  i += 2;
}

console.log(odds);

<IPython.core.display.Javascript object>

What I Changed

I changed the evens to odd to indicate that the code is finding odd numbers. Then I changed i to 1 so that it would start on a odd number. Then I replaced all the other evens varable with odds variable. Then I made sure that i is only less than 10 and not equal to it.

BELOW NOT EDITED

The intended outcome is printing a number between 1 and 100 once, if it is a multiple of 2 or 5

  • What values are outputted incorrectly. Why?
  • Make changes to get the intended outcome.
%%js

var numbers = []
var newNumbers = []
var i = 0

while (i < 100) {
    numbers.push(i)
    i += 1
}
for (var i of numbers) {
    if (numbers[i] % 5 === 0)
        newNumbers.push(numbers[i])
    if (numbers[i] % 2 === 0)
        newNumbers.push(numbers[i])
}
console.log(newNumbers) 



<IPython.core.display.Javascript object>

Challenge

This code segment is at a very early stage of implementation.

  • What are some ways to (user) error proof this code?
  • The code should be able to calculate the cost of the meal of the user

Hint:

  • write a “single” test describing an expectation of the program of the program
  • test - input burger, expect output of burger price
  • run the test, which should fail because the program lacks that feature
  • write “just enough” code, the simplest possible, to make the test pass

Then repeat this process until you get program working like you want it to work.

%%js

var menu =  {"burger": 3.99,
         "fries": 1.99,
         "drink": 0.99}
var total = 0

//shows the user the menu and prompts them to select an item
console.log("Menu")
for (var item in menu) {
    console.log(item + "  $" + menu[item].toFixed(2)) //why is toFixed used?
}
var buy = ["burger" , "fries" , "drink"]
for(var i = 0; i < buy.length; i++) {
   total = total+menu[buy[i]]
}

console.log("Your total is: $" + total.toFixed(2) + "your items are: " + buy)

 
   
  
  
  
  

<IPython.core.display.Javascript object>

Hacks

  • Fix the errors in the first three segments in this notebook and say what you changed in the code cell under “What I Changed” (Challenge is optional)