Manchester | 26-ITP-Sep | Mathew Shaibu | Sprint 2 | Module data group sprint 2

Sprint-2/debug/address.js

@@ -1,8 +1,8 @@
 // Predict and explain first...
 
-// This code should log out the houseNumber from the address object
-// but it isn't working...
-// Fix anything that isn't working
+// Answer:
+// The address in the code is an object not an array,
+// it wont log out because we try to use the array syntax instead of the object syntax
 
 const address = {
   houseNumber: 42,
@@ -12,4 +12,4 @@ const address = {
   postcode: "XYZ 123",
 };
 
-console.log(`My house number is ${address[0]}`);
+console.log(`My house number is ${address.houseNumber}`);

Sprint-2/debug/author.js

@@ -1,7 +1,7 @@
 // Predict and explain first...
 
-// This program attempts to log out all the property values in the object.
-// But it isn't working. Explain why first and then fix the problem
+// Answer:
+// A plain object is not iterable, so 'for...of cannot loop over author directly
 
 const author = {
   firstName: "Zadie",
@@ -11,6 +11,6 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
+for (const value of Object.values(author)) {
   console.log(value);
 }

Sprint-2/debug/recipe.js

@@ -1,8 +1,7 @@
 // Predict and explain first...
 
-// This program should log out the title, how many it serves and the ingredients.
-// Each ingredient should be logged on a new line
-// How can you fix it?
+// The program won't print the ingredients because it wasn't called on line 14
+
 
 const recipe = {
   title: "bruschetta",
@@ -12,4 +11,5 @@ const recipe = {
 
 console.log(`${recipe.title} serves ${recipe.serves}
   ingredients:
-${recipe}`);
+${recipe.ingredients.join("\n")}`);
+

Sprint-2/implement/contains.js

@@ -1,3 +1,8 @@
-function contains() {}
+function contains(object, property) {
+  if (typeof object !== "object" || object === null || Array.isArray(object)) {
+    throw new Error("contains requires an object");
+  }
+  return property in object;
+}
 
 module.exports = contains;

Sprint-2/implement/contains.test.js

@@ -1,40 +1,17 @@
 const contains = require("./contains.js");
 
-/*
-Implement a function called contains that checks an object contains a
-particular property
+test("contains on empty object returns false", () => {
+  expect(contains({}, "a")).toBe(false);
+});
 
-E.g. contains({a: 1, b: 2}, 'a') // returns true
-as the object contains a key of 'a'
+test("contains an object with existing property, return true", () => {
+  expect(contains({ a: 1, b: 2 }, "a")).toBe(true);
+});
 
-E.g. contains({a: 1, b: 2}, 'c') // returns false
-as the object doesn't contains a key of 'c'
+test("contains an object with missing property, return false", () => {
+  expect(contains({ a: 1, b: 2 }, "c")).toBe(false);
+});
 
-E.g. contains([1, 2, 3], 'a') throws Error("contains requires an object")
-as an array isn't an object
-*/
-
-// Acceptance criteria:
-
-// 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
-
-// Given an empty object
-// When passed to contains
-// Then it should return false
-test.todo("contains on empty object returns false");
-
-// Given an object with properties
-// When passed to contains with an existing property name
-// Then it should return true
-
-// Given an object with properties
-// When passed to contains with a non-existent property name
-// Then it should return false
-
-// Given a value that isn't an object - an array, a string, a number,
-// null, or no argument at all
-// When passed to contains
-// Then it should throw Error("contains requires an object")
-// (careful: typeof [] and typeof null are both "object")
+test("contains throws for an array", () => {
+  expect(() => contains([1, 2, 3], "a")).toThrow("contains requires an object");
+});

Sprint-2/implement/lookup.js

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

Sprint-2/implement/lookup.test.js

@@ -1,35 +1,10 @@
 const createLookup = require("./lookup.js");
 
-test.todo("creates a country currency code lookup for multiple codes");
-
-/*
-
-Create a lookup object of key value pairs from an array of code pairs
-
-Acceptance Criteria:
-
-Given
- - An array of arrays representing country code and currency code pairs
-   e.g. [['US', 'USD'], ['CA', 'CAD']]
-
-When
- - createLookup function is called with the country-currency array as an argument
-
-Then
- - It should return an object where:
- - The keys are the country codes
- - The values are the corresponding currency codes
-
-Example
-Given: [['US', 'USD'], ['CA', 'CAD']]
-
-When
-createLookup(countryCurrencyPairs) is called
-
-Then
-It should return:
- {
-   'US': 'USD',
-   'CA': 'CAD'
- }
-*/
+test("creates a country currency code lookup for multiple codes", () => {
+  expect(
+    createLookup([
+      ["US", "USD"],
+      ["CA", "CAD"],
+    ])
+  ).toEqual({ US: "USD", CA: "CAD" });
+});

Sprint-2/implement/querystring.js

@@ -1,15 +1,26 @@
 function parseQueryString(queryString) {
   const queryParams = {};
-  if (queryString.length === 0) {
-    return queryParams;
-  }
-  const keyValuePairs = queryString.split("&");
 
-  for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
-    queryParams[key] = value;
-  }
+  for (const pair of queryString.split("&")) {
+    if (pair === "") continue;
+
+    const eq = pair.indexOf("=");
+    const key = eq === -1 ? pair : pair.slice(0, eq);
+    const value = eq === -1 ? "" : pair.slice(eq + 1);
 
+    const k = decodeURIComponent(key.split("+").join(" "));
+    const v = decodeURIComponent(value.split("+").join(" "));
+
+    if (k in queryParams) {
+      if (Array.isArray(queryParams[k])) {
+        queryParams[k].push(v);
+      } else {
+        queryParams[k] = [queryParams[k], v];
+      }
+    } else {
+      queryParams[k] = v;
+    }
+  }
   return queryParams;
 }
 

Sprint-2/implement/querystring.test.js

@@ -37,12 +37,17 @@ test("should replace '+' by ' '", () => {
   });
 });
 
-// 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({
     key: ["value1", "value2", "value3"],
     foo: "bar",
   });
 });
+
+test("returns an empty query string", () => {
+  expect(parseQueryString("")).toEqual({});
+});
+
+test("handles a value with both + and percent-encoding", () => {
+  expect(parseQueryString("q=a+b%26c")).toEqual({q: "a b&c"});
+});

Sprint-2/implement/tally.js

@@ -1,3 +1,14 @@
-function tally() {}
+function tally(list) {
+  if (!Array.isArray(list)) {
+    throw new Error("tally requires an array");
+  }
+
+  const counts = {};
+
+  for (const item of list) {
+    counts[item] = (counts[item] || 0) + 1;
+  }
+  return counts;
+}
 
 module.exports = tally;

Sprint-2/implement/tally.test.js

@@ -1,34 +1,17 @@
 const tally = require("./tally.js");
 
-/**
- * tally array
- *
- * In this task, you'll need to implement a function called tally
- * that will take a list of items and count the frequency of each item
- * in an array
- *
- * For example:
- *
- * tally(['a']), target output: { a: 1 }
- * tally(['a', 'a', 'a']), target output: { a: 3 }
- * tally(['a', 'a', 'b', 'c']), target output: { a : 2, b: 1, c: 1 }
- */
 
-// Acceptance criteria:
+test("tally on an empty array returns an empty object", () => {
+  expect(tally([])).toEqual({});
+});
 
-// Given a function called tally
-// When passed an array of items
-// Then it should return an object containing the count for each unique item
+test("tally counts duplicate items", () => {
+  expect(tally(["a", "a", "a"])).toEqual({ a: 3 });
+  expect(tally(["a", "a", "b", "c"])).toEqual({ a: 2, b: 1, c: 1 });
+});
 
-// 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");
-
-// 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, a number, or no argument at all
-// When passed to tally
-// Then it should throw Error("tally requires an array")
+test("tally throws for invalid input", () => {
+  expect(() => tally("banana")).toThrow("tally requires an array");
+  expect(() => tally(42)).toThrow("tally requires an array");
+  expect(() => tally()).toThrow("tally requires an array");
+});

Sprint-2/interpret/invert.js

@@ -10,20 +10,35 @@ function invert(obj) {
   const invertedObj = {};
 
   for (const [key, value] of Object.entries(obj)) {
-    invertedObj.key = value;
+    invertedObj[value] = key;
   }
 
   return invertedObj;
 }
 
+module.exports = invert;
+
 // a) What is the current return value when invert is called with { a : 1 }
 
+// Answer: {key: 1}
+
 // b) What is the current return value when invert is called with { a: 1, b: 2 }
 
+// Answer: {key: 2}
+
 // c) What is the target return value when invert is called with {a : 1, b: 2}
 
+// Answer: target is {"1": "a", "2": "b"}
+
 // c) What does Object.entries return? Why is it needed in this program?
 
+// Answer: Object.entries returns an array of [key, value] pairs, like [["a", 1]], ["b", 2], so the loop can grab both at once
+
 // d) Explain why the current return value is different from the target output
 
+// Answer: invertedObj.key = value writes a property literally named "key" on -
+// every pass, so each pairs overwrites the same one and only the last value survives
+
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)
+
+// Answer: use brackets so the value becomes the new key: invertedObj[value] = key

Sprint-2/interpret/invert.test.js

@@ -0,0 +1,13 @@
+const invert = require("./invert.js");
+
+test("swaps key with values", () => {
+  expect(invert({ x: 10, y: 20 })).toEqual({ 10: "x", 20: "y" });
+});
+
+test("handles single entry", () => {
+  expect(invert({ a: 1 })).toEqual({ 1: "a" });
+});
+
+test("handles an empty object", () => {
+  expect(invert({})).toEqual({});
+});