London | 25-ITP-May | Houssam Lahlah | Sprint 2 | Sprint-2 #786

HoussamLh · 2025-09-13T13:56:11Z

Self checklist

I have titled my PR with Region | Cohort | FirstName LastName | Sprint | Assignment Title
My changes meet the requirements of the task
I have tested my changes
My changes follow the style guide

Changelist

1. Debug

Fixed issues in object property access and iteration:
Correctly logged object property values (author object)
Accessed specific properties instead of using incorrect indices (address object)
Logged array items within objects properly (recipe object)
Explanations and predictions added as comments in the code.

2. Implement

Implemented functions with corresponding tests:
contains(obj, prop) → checks if an object contains a specific property
createLookup(pairs) → builds a key-value lookup from an array of pairs
parseQueryString(queryString) → parses URL query strings, handles = in values, duplicates, and percent-decoding
tally(items) → counts occurrences of each item in an array
All tests cover normal cases and edge cases.

3. Interpret

invert(obj) → swaps keys and values of an object
Answers to questions (a → e) are included as comments explaining the original problem and the fix.

4. Stretch

countWords(str) → counts word occurrences in a string
Advanced: removes punctuation, ignores case, sorts results by frequency
calculateMode(list) → returns the most frequent number
Refactored into helper functions: buildFrequencyMap and findMode
totalTill(till) → calculates the total value of a till in pounds
Fixed parsing of coin strings (e.g., "50p" → 50), handles empty till
Tests added for all functions to validate expected behavior and edge cases.

Questions

Why did for (const value of author) fail when iterating over an object?
How does contains(obj, prop) check for the existence of a property?
Why did invert({ a: 1, b: 2 }) originally return { key: 2 } instead of { "1": "a", "2": "b" }?
Why did totalTill originally return NaN when multiplying coin * quantity?

Challenge Notes
1. Iterating over objects

I tried for (const value of author) but it failed because plain objects are not iterable.
Fix: use for...in for keys, or Object.keys() / Object.values() / Object.entries() with for...of.

2. contains(obj, prop) behavior

At first, I used Object.prototype.hasOwnProperty.call(obj, prop) to check for own properties.
Mentor suggested the cleaner Object.hasOwn(obj, prop).
Assumption: contains() should check own properties only, not inherited ones.

3. invert({ a: 1, b: 2 }) bug

The original code returned { key: 2 } because I mistakenly wrote result.key = obj[key].
Dot notation created a literal "key" property instead of using the variable.
Fix: use bracket notation → result[obj[key]] = key;.

4. totalTill returning NaN

The expression coin * quantity failed because coin was a string like "20p".
Multiplying "20p" * 3 results in NaN.
Fix: parse the coin into a number first:
const coinValue = parseInt(coin, 10);
total += coinValue * quantity;

…ests

… keys, duplicates and leading '?'

cjyuan

Code is very solid! I only have a few suggestions.

cjyuan · 2025-09-13T23:04:39Z

Sprint-2/implement/contains.js

+  }
+
+  // Use Object.prototype.hasOwnProperty to check if property exists
+  return Object.prototype.hasOwnProperty.call(obj, prop);


There is another (more compact) function in Object we can use. Can you find out how we can rewrite line 8 with less code.

Hi cjyuan,
Thank you for the feedback!
I updated the code to use Object.hasOwn(obj, prop) instead of Object.prototype.hasOwnProperty.call(obj, prop).
It’s definitely more compact and readable.

cjyuan · 2025-09-13T23:16:20Z

Sprint-2/implement/tally.js

+  const result = {};
+  for (const item of items) {
+    if (Object.prototype.hasOwnProperty.call(result, item)) {


There is a way to create an empty object with no inherited properties.

If result is such an object, then we can simplify line 8 as if (result[item]) {.

Hi cjyuan,
Thank you for pointing this out!
I changed result = {} to result = Object.create(null), so the object has no inherited properties. This allowed me to simplify the condition to if (result[item]) { as suggested.

cjyuan · 2025-09-13T23:23:51Z

Sprint-2/stretch/count-words.js

+  const counts = {};
+
+  // 1. Remove punctuation
+  const noPunctuation = str.replace(/[.,!?]/g, "");
+
+  // 2. Ignore case
+  const words = noPunctuation.toLowerCase().split(/\s+/);
+
+  for (const word of words) {
+    if (!word) continue; // skip empty strings
+    counts[word] = (counts[word] || 0) + 1;
+  }


Can you check if this function returns what you expect in the following function call?

countWords("constructor constructor");

Hi cjyuan,
Thanks for your guidence.
I tested with "constructor constructor" and saw the issue. I updated counts to use Object.create(null) instead of {}, so now the function correctly returns { constructor: 2 }.

cjyuan · 2025-09-13T23:27:44Z

Sprint-2/stretch/till.js

-    total += coin * quantity;
+    // coin is a string like "1p", "20p"
+    // We need to strip the "p" and convert it into a number of pennies
+    const coinValue = parseInt(coin.replace("p", ""), 10);


We could also rewrite line 13 as:
const coinValue = parseInt(coin);

Can you figure out why?

Hi cjyuan,
Thanks! I see why — parseInt("20p", 10) returns 20 since it stops parsing at the "p".
That makes .replace("p", "") unnecessary, so I simplified the code.

cjyuan · 2025-09-14T12:39:48Z

Why did for (const value of author) fail when iterating over an object?

Have you try asking AI?

How does contains(obj, prop) check for the existence of a property?

The spec was not clear how contains() should check for the existence of a property. When the spec is not clear, we can either ask for clarification (especially when the ambiguity can lead to serious consequence) or make reasonable assumption and write down our assumption.

Why did invert({ a: 1, b: 2 }) originally return { key: 2 } instead of { "1": "a", "2": "b" }?

It seems you had figured out the answer.

Why did totalTill originally return NaN when multiplying coin * quantity?

You can also try AI for questions like this. :)

…structor

cjyuan · 2025-09-14T21:40:10Z

Everything looks great. Well done!

HoussamLh added 11 commits September 13, 2025 00:13

Fix address logging: use houseNumber key instead of numeric index

5042174

Fix object iteration: use Object.values() to loop over author values

2354307

Fix recipe logging: print ingredients on separate lines

03b7641

Implement contains function with tests to check object properties

57d9de0

Implement createLookup to build country-currency lookup object with t…

e198282

…ests

Fix parseQueryString: split on first '='; decode values; handle empty…

e65e951

… keys, duplicates and leading '?'

Implement tally function to count array item frequencies with tests

532a449

Interpret invert: explain issues, fix implementation, and add tests

93287a2

feat: implement countWords function with advanced version

1ecf7e9

refactor: split calculateMode into smaller functions

3b8b322

fix: correct totalTill to calculate coin values properly

d78a59b

HoussamLh added the Needs Review Trainee to add when requesting review. PRs without this label will not be reviewed. label Sep 13, 2025

HoussamLh mentioned this pull request Sep 13, 2025

London ITP May 25 | Data groups | Houssam Lahlah HoussamLh/My-Coursework-Planner#51

Open

cjyuan reviewed Sep 13, 2025

View reviewed changes

cjyuan added Reviewed Volunteer to add when completing a review with trainee action still to take. and removed Needs Review Trainee to add when requesting review. PRs without this label will not be reviewed. labels Sep 13, 2025

HoussamLh added 4 commits September 14, 2025 21:36

Replace hasOwnProperty.call with Object.hasOwn for clarity

50f1300

Use Object.create(null) to simplify tally condition

8eda17c

Use Object.create(null) in countWords to handle special keys like con…

be61ded

…structor

Simplify coin parsing by using parseInt directly

91480e4

HoussamLh added Needs Review Trainee to add when requesting review. PRs without this label will not be reviewed. and removed Reviewed Volunteer to add when completing a review with trainee action still to take. labels Sep 14, 2025

cjyuan added Complete Volunteer to add when work is complete and all review comments have been addressed. and removed Needs Review Trainee to add when requesting review. PRs without this label will not be reviewed. labels Sep 14, 2025

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

Uh oh!

London | 25-ITP-May | Houssam Lahlah | Sprint 2 | Sprint-2 #786

London | 25-ITP-May | Houssam Lahlah | Sprint 2 | Sprint-2 #786

Uh oh!

HoussamLh commented Sep 13, 2025 •

edited

Loading

Uh oh!

cjyuan left a comment

Uh oh!

cjyuan Sep 13, 2025

Uh oh!

HoussamLh Sep 14, 2025

Uh oh!

cjyuan Sep 13, 2025

Uh oh!

HoussamLh Sep 14, 2025

Uh oh!

cjyuan Sep 13, 2025

Uh oh!

HoussamLh Sep 14, 2025

Uh oh!

cjyuan Sep 13, 2025

Uh oh!

HoussamLh Sep 14, 2025

Uh oh!

cjyuan commented Sep 14, 2025

Uh oh!

cjyuan commented Sep 14, 2025

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

Uh oh!

London | 25-ITP-May | Houssam Lahlah | Sprint 2 | Sprint-2 #786

Are you sure you want to change the base?

London | 25-ITP-May | Houssam Lahlah | Sprint 2 | Sprint-2 #786

Uh oh!

Conversation

HoussamLh commented Sep 13, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

cjyuan left a comment

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

cjyuan commented Sep 14, 2025

Uh oh!

cjyuan commented Sep 14, 2025

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

HoussamLh commented Sep 13, 2025 •

edited

Loading