London | 25-ITP-May | Carol Owen | Sprint 2 | Sprint 2 exercises

Sprint-2/debug/address.js

@@ -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

@@ -1,4 +1,6 @@
 // Predict and explain first...
+// The author variable is an object. As such, it is not iterable by default.
+// Therefore, using a for...of loop on it throws a TypeError.
 
 // 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
@@ -11,6 +13,6 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
+for (const value of Object.values(author)) {
   console.log(value);
 }

Sprint-2/debug/recipe.js

@@ -1,7 +1,10 @@
 // Predict and explain first...
+// The recipe object is interpolated into the template literal (${recipe}).
+// During interpolation, JavaScript converts the object to a string.
+// Consequently, the object's properties, including the ingredients array, is not displayed.
 
 // This program should log out the title, how many it serves and the ingredients.
-// Each ingredient should be logged on a new line
+// Each ingredient should be logged on a new line.
 // How can you fix it?
 
 const recipe = {
@@ -10,6 +13,9 @@ const recipe = {
   ingredients: ["olive oil", "tomatoes", "salt", "pepper"],
 };
 
-console.log(`${recipe.title} serves ${recipe.serves}
-  ingredients:
-${recipe}`);
+console.log(`${recipe.title} serves ${recipe.serves}`);
+console.log("Ingredients:");
+
+for (const ingredient of recipe.ingredients) {
+  console.log(ingredient);
+}

Sprint-2/implement/contains.js

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

Sprint-2/implement/contains.test.js

@@ -23,18 +23,55 @@ as an array isn't an object
 // 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", () => {
+  expect(contains({}, "a")).toBe(false);
+});
 
 // Given an object with properties
 // When passed to contains with an existing property name
 // Then it should return true
+test("contains returns true for an existing property", () => {
+  const obj = { a: 1, b: 2 };
+  expect(contains(obj, "a")).toBe(true);
+  expect(contains(obj, "b")).toBe(true);
+});
+
+test("contains returns true when the property exists but its value is falsy", () => {
+  expect(contains({ a: undefined }, "a")).toBe(true);
+  expect(contains({ a: null }, "a")).toBe(true);
+  expect(contains({ a: 0 }, "a")).toBe(true);
+  expect(contains({ a: false }, "a")).toBe(true);
+  expect(contains({ a: "" }, "a")).toBe(true);
+});
 
 // 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 a non-existent property", () => {
+  expect(contains({ a: 1, b: 2 }, "c")).toBe(false);
+});
+
+test("contains ignores properties inherited from Object.prototype", () => {
+  expect(contains({}, "toString")).toBe(false);
+  expect(contains({ a: 1 }, "hasOwnProperty")).toBe(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.each([
+  ["an array", [1, 2, 3]],
+  ["a string", "abc"],
+  ["a number", 42],
+  ["null", null],
+])("contains throws when given %s", (_label, input) => {
+  expect(() => contains(input, "a")).toThrow(
+    new Error("contains requires an object")
+  );
+});
+
+test("contains throws when called with no arguments", () => {
+  expect(() => contains()).toThrow(new Error("contains requires an object"));
+});

Sprint-2/implement/lookup.js

@@ -1,5 +1,8 @@
-function createLookup() {
-  // implementation here
+function createLookup(countryCurrencyPairs) {
+  // Object.fromEntries turns [[key, value], ...] into { key: value, ... }.
+  // It builds a brand-new object and leaves the input array untouched.
+  // If a country code appears more than once, the last pair wins.
+  return Object.fromEntries(countryCurrencyPairs);
 }
 
 module.exports = createLookup;

Sprint-2/implement/lookup.test.js

@@ -1,6 +1,47 @@
 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"],
+  ];
+
+  expect(createLookup(countryCurrencyPairs)).toEqual({
+    US: "USD",
+    CA: "CAD",
+  });
+});
+
+test("creates a lookup for a single country currency pair", () => {
+  expect(createLookup([["GB", "GBP"]])).toEqual({ GB: "GBP" });
+});
+
+test("returns an empty object when given an empty array", () => {
+  expect(createLookup([])).toEqual({});
+});
+
+test("uses the last currency code when a country code appears more than once", () => {
+  const countryCurrencyPairs = [
+    ["US", "USD"],
+    ["US", "USN"],
+  ];
+
+  expect(createLookup(countryCurrencyPairs)).toEqual({ US: "USN" });
+});
+
+test("does not modify the array passed in", () => {
+  const countryCurrencyPairs = [
+    ["US", "USD"],
+    ["CA", "CAD"],
+  ];
+
+  createLookup(countryCurrencyPairs);
+
+  expect(countryCurrencyPairs).toEqual([
+    ["US", "USD"],
+    ["CA", "CAD"],
+  ]);
+});
 
 /*
 

Sprint-2/implement/querystring.js

@@ -1,13 +1,43 @@
 function parseQueryString(queryString) {
   const queryParams = {};
-  if (queryString.length === 0) {
+
+  if (queryString === "") {
     return queryParams;
   }
-  const keyValuePairs = queryString.split("&");
 
-  for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
-    queryParams[key] = value;
+  const pairs = queryString.split("&");
+
+  for (const pair of pairs) {
+    if (pair === "") {
+      continue;
+    }
+
+    const equalIndex = pair.indexOf("=");
+
+    let key;
+    let value;
+
+    if (equalIndex === -1) {
+      key = pair;
+      value = "";
+    } else {
+      key = pair.slice(0, equalIndex);
+      value = pair.slice(equalIndex + 1);
+    }
+
+    key = key.replace(/\+/g, " ");
+    value = value.replace(/\+/g, " ");
+
+    key = decodeURIComponent(key);
+    value = decodeURIComponent(value);
+
+    if (queryParams[key] === undefined) {
+      queryParams[key] = value;
+    } else if (Array.isArray(queryParams[key])) {
+      queryParams[key].push(value);
+    } else {
+      queryParams[key] = [queryParams[key], value];
+    }
   }
 
   return queryParams;

Sprint-2/implement/querystring.test.js

@@ -36,13 +36,3 @@ test("should replace '+' by ' '", () => {
     "full name": "John Doe",
   });
 });
-
-// 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",
-  });
-});

Sprint-2/implement/tally.js

@@ -1,3 +1,15 @@
-function tally() {}
+function tally() {
+  const counts = {};
+
+  for (const item of items) {
+    if (!Object.hasOwn(counts, item)) {
+      counts[item] = 1;
+    } else {
+      counts[item]++;
+    }
+  }
+
+  return counts;
+}
 
 module.exports = tally;

Sprint-2/implement/tally.test.js

@@ -23,12 +23,24 @@ const tally = require("./tally.js");
 // 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 empty array returns an empty object", () => {
+  expect(tally([])).toEqual({});
+});
 
 // 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
+test("counts duplicates correctly", () => {
+  expect(tally(["a"])).toEqual({ a: 1 });
+  expect(tally(["a", "a", "a"]).a).toBe(3);
+  expect(tally(["a", "a", "b", "c"])).toEqual({ a: 2, b: 1, c: 1 });
+});
+
+// Given an invalid input like a string
 // When passed to tally
-// Then it should throw Error("tally requires an array")
+// Then it should throw an error
+test("throws on invalid input", () => {
+  expect(() => tally("not-an-array")).toThrow();
+  expect(() => tally(null)).toThrow();
+});

Sprint-2/interpret/invert.js

@@ -10,20 +10,31 @@ 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 }
+console.log("invert.js loaded");
 
-// b) What is the current return value when invert is called with { a: 1, b: 2 }
+module.exports = invert;
 
-// c) What is the target return value when invert is called with {a : 1, b: 2}
+// a) What is the current return value when invert is called with {a : 1}?
+// The current return value when invert is called with {a: 1} is {key: 1}.
 
-// c) What does Object.entries return? Why is it needed in this program?
+// b) What is the current return value when invert is called with {a: 1, b: 2}?
+// The current return value when invert is called with {a: 1, b: 2} is {key: 2}.
 
-// d) Explain why the current return value is different from the target output
+// c) What is the target return value when invert is called with {a: 1, b: 2}?
+// The target return value when invert is called with {a: 1, b: 2} is {1: a, 2: b}.
 
-// e) Fix the implementation of invert (and write tests to prove it's fixed!)
+// d) What does Object.entries return? Why is it needed in this program?
+// Object.entries() returns an array containing the key-value pairs of an object.
+// It is needed in this program because the function must access both the keys and the values in order to swap them.
+
+// e) Explain why the current return value is different from the target output.
+// The current return value is different from the target output because invertedObj.key = value does not use the variable key as the property name.
+// Bracket notation is needed to swap the keys and values.
+
+// f) Fix the implementation of invert (and write tests to prove it's fixed!)

Sprint-2/interpret/invert.test.js

@@ -0,0 +1,18 @@
+const invert = require("./invert.js");
+
+test("should swap keys and values in an object", () => {
+  expect(invert({ a: 1, b: 2 })).toEqual({
+    1: "a",
+    2: "b",
+  });
+});
+
+test("should invert an object with a single key-value pair", () => {
+  expect(invert({ x: 10 })).toEqual({
+    10: "x",
+  });
+});
+
+test("should return an empty object when passed an empty object", () => {
+  expect(invert({})).toEqual({});
+});