Cape Town | 26-ITP-May| Enice Mutanda| Sprint 2| Data objects

Sprint-2/implement/contains.js

@@ -1,3 +1,6 @@
-function contains() {}
+function contains(obj, prop) {
+ if (typeof obj !== "object" || obj === null) return false;
+ return Object.prototype.hasOwnProperty.call(obj, prop);
+}
 
-module.exports = contains;
+module.exports = contains;

Sprint-2/implement/contains.test.js

@@ -1,4 +1,4 @@
-const contains = require("./contains.js");
+const contains = require("./contains")
 
 /*
 Implement a function called contains that checks an object contains a
@@ -16,20 +16,44 @@ as the object doesn't contains a key of 'c'
 // Given a contains function
 // When passed an object and a property name
 // Then it should return true if the object contains the property, false otherwise
+test("contains returns true for existing property", () => {
+const currentOutput = contains({a:1,b:2}, 'a');
+const targetOutput = true;
+expect(currentOutput).toEqual(targetOutput); 
+});
 
 // Given an empty object
 // When passed to contains
 // Then it should return false
-test.todo("contains on empty object returns false");
+test("contains on empty object returns false", () => {
+const currentOutput = contains({}, 'a');
+const targetOutput = false;
+expect(currentOutput).toEqual(targetOutput); 
+});
 
 // Given an object with properties
 // When passed to contains with an existing property name
 // Then it should return true
+test("contains returns true for existing property", () => {
+const currentOutput = contains({a:1,b:2}, 'b');
+const targetOutput = true;
+expect(currentOutput).toEqual(targetOutput); 
+}); 
 
 // Given an object with properties
 // When passed to contains with a non-existent property name
 // Then it should return false
+test("contains returns false for non-existent property", () => {
+const currentOutput = contains({a:1,b:2}, 'c');
+const targetOutput = false;
+expect(currentOutput).toEqual(targetOutput); 
+});
 
 // Given invalid parameters like an array
 // When passed to contains
 // Then it should return false or throw an error
+test("contains returns false for invalid parameters", () => {
+const currentOutput = contains([1,2,3], 'a');
+const targetOutput = false;
+expect(currentOutput).toEqual(targetOutput); 
+});

Sprint-2/implement/lookup.js

@@ -1,5 +1,9 @@
-function createLookup() {
- // implementation here
+function createLookup(pairs) {
+ const lookup = {};
+ for (const [countryCode, currencyCode] of pairs) {
+ lookup[countryCode] = currencyCode;
+ }
+ return lookup;
 }
 
-module.exports = createLookup;
+module.exports = createLookup;

Sprint-2/implement/lookup.test.js

@@ -1,7 +1,10 @@
 const createLookup = require("./lookup.js");
 
-test.todo("creates a country currency code lookup for multiple codes");
-
+test("creates a country currency code lookup for multiple codes", () => {
+ const countryCurrencyPairs = [["US", "USD"], ["CA", "CAD"]];
+ const result = createLookup(countryCurrencyPairs);
+ expect(result).toEqual({ US: "USD", CA: "CAD" });
+});
 /*
 
 Create a lookup object of key value pairs from an array of code pairs

Sprint-2/implement/querystring.js

@@ -1,16 +1,24 @@
+function decodeComponent(str) {
+ return decodeURIComponent(str.replaceAll("+", " "));
+}
+
 function parseQueryString(queryString) {
- const queryParams = {};
  if (queryString.length === 0) {
- return queryParams;
+ return {};
  }
- const keyValuePairs = queryString.split("&");
 
- for (const pair of keyValuePairs) {
- const [key, value] = pair.split("=");
- queryParams[key] = value;
+ const params = {};
+ const pairs = queryString.split("&").filter((pair) => pair !== "");
+
+ for (const pair of pairs) {
+ const [rawKey, ...rawValueParts] = pair.split("=");
+ const key = decodeComponent(rawKey);
+ const value = decodeComponent(rawValueParts.join("="));
+
+ params[key] = key in params ? [].concat(params[key], value) : value;
  }
 
- return queryParams;
+ return params;
 }
 
-module.exports = parseQueryString;
+module.exports = parseQueryString;

Sprint-2/implement/querystring.test.js

@@ -3,7 +3,7 @@
 // Below are some test cases the implementation doesn't handle well.
 // Fix the implementation for these tests, and try to think of as many other edge cases as possible - write tests and fix those too.
 
-const parseQueryString = require("./querystring.js")
+const parseQueryString = require("./querystring");
 
 test("should parse values containing '='", () => {
  expect(parseQueryString("equation=a=b-2")).toEqual({
@@ -37,12 +37,18 @@ test("should replace '+' by ' '", () => {
  });
 });
 
+test("should return {} for an empty string", () => {
+ expect(parseQueryString("")).toEqual({});
+});
+
 // Stretch exercise: Handling query strings that contain identical keys
 
 // Delete this test if you are not working on this optional case
 test("should store values of a key in an array when the key has 2 or more values", () => {
- expect(parseQueryString("key=value1&key=value2&key=value3&foo=bar")).toEqual({
+ expect(
+ parseQueryString("key=value1&key=value2&key=value3&foo=bar")
+ ).toEqual({
  key: ["value1", "value2", "value3"],
  foo: "bar",
  });
-});
+});

Sprint-2/implement/tally.js

@@ -1,3 +1,13 @@
-function tally() {}
+function tally(arr) {
+ if (!Array.isArray(arr)) {
+ throw new Error("tally expects an array");
+ }
 
-module.exports = tally;
+ const counts = {};
+ for (const item of arr) {
+ counts[item] = (counts[item] || 0) + 1;
+ }
+ return counts;
+}
+
+module.exports = tally;

Sprint-2/implement/tally.test.js

@@ -14,21 +14,22 @@ const tally = require("./tally.js");
  * tally(['a', 'a', 'b', 'c']), target output: { a : 2, b: 1, c: 1 }
  */
 
-// Acceptance criteria:
 
 // Given a function called tally
 // When passed an array of items
 // Then it should return an object containing the count for each unique item
+describe("tally on an array of items returns counts for each unique item", () => {
+ test("tally on an empty array returns an empty object", () => {
+ expect(tally([])).toEqual({});
+ });
 
-// Given an empty array
-// When passed to tally
-// Then it should return an empty object
-test.todo("tally on an empty array returns an empty object");
+ test("tally on an array with duplicate items returns counts for each unique item", () => {
+ expect(tally(["a"])).toEqual({ a: 1 });
+ expect(tally(["a", "a", "a"])).toEqual({ a: 3 });
+ expect(tally(["a", "a", "b", "c"])).toEqual({ a: 2, b: 1, c: 1 });
+ });
 
-// Given an array with duplicate items
-// When passed to tally
-// Then it should return counts for each unique item
-
-// Given an invalid input like a string
-// When passed to tally
-// Then it should throw an error
+ test("tally throws an error for invalid input", () => {
+ expect(() => tally("not an array")).toThrow();
+ });
+});

Sprint-2/interpret/invert.js

@@ -1,29 +1,60 @@
 // Let's define how invert should work
-
+// inverse typically means to reverse the key and value in an object.
 // Given an object
 // When invert is passed this object
 // Then it should swap the keys and values in the object
-
 // E.g. invert({x : 10, y : 20}), target output: {"10": "x", "20": "y"}
 
+// The original buggy implementation looked like this:
+
+// function invert(obj) {
+// const invertedObj = {};
+// for (const [key, value] of Object.entries(obj)) {
+// invertedObj.key = value;
+// }
+// return invertedObj;
+// }
+
+// a) What is the current return value when invert is called with { a: 1 }?
+// -> { key: 1 }
+// Only invertedObj.key = value runs, setting a property literally
+// named "key" to 1. There is no swap line, so no "1": "a" pair
+// is ever added.
+
+// b) What is the current return value when invert is called with { a: 1, b: 2 }?
+// -> { key: 2 }
+// Each loop iteration overwrites the same literal "key" property.
+// First a: key becomes 1, then b: key gets overwritten to 2.
+// No other properties are ever added, since there's no line that
+// writes to invertedObj[value].
+
+// c) What is the target return value when invert is called with { a: 1, b: 2 }?
+// -> { "1": "a", "2": "b" }
+
+// c) What does Object.entries return, and why is it needed?
+// -> Object.entries(obj) returns an array of [key, value] pairs, e.g.
+// [["a", 1], ["b", 2]]. It's needed because a for...of loop can't
+// iterate directly over an object's properties - Object.entries
+// converts the object into something iterable, and array
+// destructuring ([key, value]) lets us pull out both parts at once.
+
+// d) Why is the current return value different from the target output?
+// -> Two problems: (1) invertedObj.key uses dot notation with the
+// literal word "key", so it always writes to a property called
+// "key" rather than using the loop variable's value. (2) The line
+// that would actually perform the inversion - invertedObj[value] = key -
+// is missing entirely, so the object is never built up with the
+// swapped key/value pairs.
+
+// e) Fix: replace invertedObj.key = value with invertedObj[value] = key,
+// using bracket notation so the loop variable's value is used as the
+// property name. See invert.test.js for tests proving the fix works.
 function invert(obj) {
  const invertedObj = {};
-
  for (const [key, value] of Object.entries(obj)) {
- invertedObj.key = value;
+ invertedObj[value] = key;
  }
-
  return invertedObj;
 }
 
-// a) What is the current return value when invert is called with { a : 1 }
-
-// b) What is the current return value when invert is called with { a: 1, b: 2 }
-
-// c) What is the target return value when invert is called with {a : 1, b: 2}
-
-// c) What does Object.entries return? Why is it needed in this program?
-
-// d) Explain why the current return value is different from the target output
-
-// e) Fix the implementation of invert (and write tests to prove it's fixed!)
+module.exports = invert;

Sprint-2/interpret/invert.test.js

@@ -0,0 +1,17 @@
+const invert = require("./invert");
+
+test("invert swaps keys and values in an object", () => {
+ const input = { a: 1, b: 2 };
+ const expectedOutput = { "1": "a", "2": "b" };
+ expect(invert(input)).toEqual(expectedOutput);
+});
+
+test("invert returns an empty object when given an empty object", () => {
+ expect(invert({})).toEqual({});
+});
+
+test("invert works with string values", () => {
+ const input = { x: "10", y: "20" };
+ const expectedOutput = { "10": "x", "20": "y" };
+ expect(invert(input)).toEqual(expectedOutput);
+});

Sprint-2/stretch/count-words.js

@@ -1,28 +1,14 @@
-/*
- Count the number of times a word appears in a given string.
-
- Write a function called countWords that
- - takes a string as an argument
- - returns an object where
- - the keys are the words from the string and
- - the values are the number of times the word appears in the string
-
- Example
- If we call countWords like this:
-
- countWords("you and me and you") then the target output is { you: 2, and: 2, me: 1 }
-
- To complete this exercise you should understand
- - Strings and string manipulation
- - Loops
- - Comparison inside if statements
- - Setting values on an object
-
-## Advanced challenges
-
-1. Remove all of the punctuation (e.g. ".", ",", "!", "?") to tidy up the results
-
-2. Ignore the case of the words to find more unique words. e.g. (A === a, Hello === hello)
-
-3. Order the results to find out which word is the most common in the input
-*/
+function countWords(str) {
+ const wordCount = {};
+ const words = str
+ .toLowerCase()
+ .replace(/[^\w\s]/g, "")
+ .split(/\s+/)
+ .filter(Boolean);
+ for (const word of words) {
+ wordCount[word] = (wordCount[word] || 0) + 1;
+ }
+ return wordCount;
+}
+
+module.exports = countWords;

Sprint-2/stretch/count-words.test.js

@@ -0,0 +1,17 @@
+const countWords = require("./count-words");
+
+test("counts word occurrences in a string", () => {
+ expect(countWords("you and me and you")).toEqual({ you: 2, and: 2, me: 1 });
+});
+
+test("returns an empty object for an empty string", () => {
+ expect(countWords("")).toEqual({});
+});
+
+test("ignores punctuation", () => {
+ expect(countWords("Hello, world! Hello?")).toEqual({ hello: 2, world: 1 });
+});
+
+test("ignores case", () => {
+ expect(countWords("A a Hello hello")).toEqual({ a: 2, hello: 2 });
+});