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feat: add truthy and falsy exercise with solutions and tests
- Introduced a new exercise on truthy and falsy values in JavaScript. - Added corresponding solution and test files. - Updated README files to include explanations and instructions for the new exercise. - Modified package-lock.json to include new exercise dependencies.
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‎exercises/03.primitive-types/03.problem.booleans-and-comparisons/index.ts‎

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@@ -8,9 +8,6 @@ const stockCount: number = 100
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// 🐨 Create a variable `isOnSale` with type `boolean` set to `false`
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// 🐨 Create a variable `hasDiscount` that's true when price is under 50
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// 💰 Use a comparison: price < 50
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// 🐨 Create a variable `canPurchase` that's true when isAvailable AND stockCount > 0
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// 💰 Use the && operator
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@@ -23,8 +20,6 @@ console.log('Is Available:', isAvailable)
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// @ts-expect-error - 💣 remove this comment
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console.log('Is On Sale:', isOnSale)
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// @ts-expect-error - 💣 remove this comment
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console.log('Has Discount:', hasDiscount)
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// @ts-expect-error - 💣 remove this comment
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console.log('Can Purchase:', canPurchase)
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// @ts-expect-error - 💣 remove this comment
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console.log('Is Not Available:', isNotAvailable)

‎exercises/03.primitive-types/03.solution.booleans-and-comparisons/index.test.ts‎

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@@ -22,26 +22,6 @@ await test('isAvailable should be true', () => {
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)
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})
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await test('isOnSale is exported', () => {
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assert.ok(
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'isOnSale' in solution,
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'🚨 Make sure you export "isOnSale" - add: export { isAvailable, isOnSale, ... }',
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)
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})
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await test('isOnSale should be false', () => {
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assert.strictEqual(
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solution.isOnSale,
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false,
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'🚨 isOnSale should be false - check your assignment',
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)
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assert.strictEqual(
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typeof solution.isOnSale,
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'boolean',
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'🚨 isOnSale should be a boolean type - use true or false, not a string',
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)
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})
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await test('hasDiscount is exported', () => {
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assert.ok(
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'hasDiscount' in solution,

‎exercises/03.primitive-types/03.solution.booleans-and-comparisons/index.ts‎

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@@ -6,8 +6,6 @@ const stockCount: number = 100
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const isAvailable: boolean = true
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const isOnSale: boolean = false
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const hasDiscount: boolean = price < 50
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const canPurchase: boolean = isAvailable && stockCount > 0
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// ✅ Verification
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console.log('Is Available:', isAvailable)
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console.log('Is On Sale:', isOnSale)
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console.log('Has Discount:', hasDiscount)
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console.log('Can Purchase:', canPurchase)
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console.log('Is Not Available:', isNotAvailable)
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export { isAvailable, isOnSale, hasDiscount, canPurchase, isNotAvailable }
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export { isAvailable, hasDiscount, canPurchase, isNotAvailable }

‎exercises/03.primitive-types/06.problem.truthy-falsy/README.mdx‎

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# Truthy and Falsy
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👨‍💼 We often need to decide if a value "exists" without comparing it to
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`null` or `undefined`. JavaScript treats some values as **falsy**, and everything
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else as **truthy**.
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Falsy values:
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- `false`
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- `0`, `-0`, `0n`
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- `''` (empty string)
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- `null`
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- `undefined`
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- `NaN`
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You can convert any value to a boolean with `Boolean(value)` or `!!value`.
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🐨 Open <InlineFile file="index.ts" /> and:
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1. Create `hasUsername` based on the truthiness of `username`
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2. Create `hasNickname` based on the truthiness of `nickname`
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3. Create `hasAge` based on the truthiness of `age`
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4. Create `hasNotes` based on the truthiness of `notes`
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5. Create `canCheckout` that's `true` when `cartTotal` is truthy **and**
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`hasAcceptedTerms` is true
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6. Create `canCreateAccount` that's `true` when `hasUsername`, `email`, and
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`password` are all truthy
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💰 Use `Boolean(value)` or `!!value` to convert to a boolean.
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📜 [MDN - Truthy](https://developer.mozilla.org/en-US/docs/Glossary/Truthy)
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📜 [MDN - Falsy](https://developer.mozilla.org/en-US/docs/Glossary/Falsy)

‎exercises/03.primitive-types/06.problem.truthy-falsy/index.ts‎

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// Account and Checkout Status
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// Using truthy and falsy values to drive decisions
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const username = 'kent'
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const nickname = ''
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const age = 0
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const email = 'kent@epicweb.dev'
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const password = ''
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const notes = undefined
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const cartTotal = 42
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const hasAcceptedTerms = false
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// 🐨 Create a variable `hasUsername` based on the truthiness of `username`
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// 💰 Use Boolean(username) or !!username
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// 🐨 Create a variable `hasNickname` based on the truthiness of `nickname`
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// 🐨 Create a variable `hasAge` based on the truthiness of `age`
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// 🐨 Create a variable `hasNotes` based on the truthiness of `notes`
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// 🐨 Create a variable `canCheckout` that is true when cartTotal is truthy AND
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// hasAcceptedTerms is true
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// 🐨 Create a variable `canCreateAccount` that is true when hasUsername, email,
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// and password are all truthy
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// ✅ Verification
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// @ts-expect-error - 💣 remove this comment
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console.log('Has username:', hasUsername)
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// @ts-expect-error - 💣 remove this comment
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console.log('Has nickname:', hasNickname)
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// @ts-expect-error - 💣 remove this comment
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console.log('Has age:', hasAge)
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// @ts-expect-error - 💣 remove this comment
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console.log('Has notes:', hasNotes)
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// @ts-expect-error - 💣 remove this comment
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console.log('Can checkout:', canCheckout)
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// @ts-expect-error - 💣 remove this comment
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console.log('Can create account:', canCreateAccount)
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// 🐨 Export your variables so we can verify your work
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// export { hasUsername, hasNickname, hasAge, hasNotes, canCheckout, canCreateAccount }

‎exercises/03.primitive-types/06.problem.truthy-falsy/package.json‎

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{
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"name": "exercises_03.primitive-types_06.problem.truthy-falsy",
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"type": "module",
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"scripts": {
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"start": "npx @kentcdodds/log-module ./index.ts",
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"start:watch": "npx @kentcdodds/log-module --watch ./index.ts",
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"test": "node --test index.test.ts",
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"test:watch": "node --watch --test index.test.ts"
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}
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}

‎exercises/03.primitive-types/06.solution.truthy-falsy/README.mdx‎

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# Truthy and Falsy
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👨‍💼 Nice work! You just used truthy and falsy values to build boolean logic
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without writing explicit comparisons.
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🦉 Remember: a boolean can be created from **any** value:
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```ts
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const isPresent = Boolean(value)
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const alsoBoolean = !!value
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```
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This is useful when you care about "has a value" rather than the specific
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value. We'll rely on this pattern a lot when we get into control flow.

‎exercises/03.primitive-types/06.solution.truthy-falsy/index.test.ts‎

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import assert from 'node:assert/strict'
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import { test } from 'node:test'
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import * as solution from './index.ts'
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await test('hasUsername is exported', () => {
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assert.ok(
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'hasUsername' in solution,
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'🚨 Make sure you export "hasUsername" - add: export { hasUsername, ... }',
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)
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})
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await test('hasUsername should be true', () => {
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assert.strictEqual(
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typeof solution.hasUsername,
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'boolean',
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'🚨 hasUsername should be a boolean - use Boolean(username) or !!username',
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)
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assert.strictEqual(
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solution.hasUsername,
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true,
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'🚨 hasUsername should be true when username is a non-empty string',
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)
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})
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await test('hasNickname is exported', () => {
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assert.ok(
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'hasNickname' in solution,
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'🚨 Make sure you export "hasNickname" - add: export { ..., hasNickname, ... }',
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)
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})
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await test('hasNickname should be false', () => {
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assert.strictEqual(
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typeof solution.hasNickname,
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'boolean',
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'🚨 hasNickname should be a boolean - use Boolean(nickname) or !!nickname',
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)
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assert.strictEqual(
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solution.hasNickname,
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false,
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'🚨 hasNickname should be false when nickname is an empty string',
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)
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})
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await test('hasAge is exported', () => {
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assert.ok(
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'hasAge' in solution,
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'🚨 Make sure you export "hasAge" - add: export { ..., hasAge, ... }',
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)
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})
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await test('hasAge should be false', () => {
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assert.strictEqual(
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typeof solution.hasAge,
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'boolean',
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'🚨 hasAge should be a boolean - use Boolean(age) or !!age',
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)
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assert.strictEqual(
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solution.hasAge,
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false,
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'🚨 hasAge should be false when age is 0',
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)
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})
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await test('hasNotes is exported', () => {
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assert.ok(
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'hasNotes' in solution,
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'🚨 Make sure you export "hasNotes" - add: export { ..., hasNotes, ... }',
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)
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})
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await test('hasNotes should be false', () => {
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assert.strictEqual(
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typeof solution.hasNotes,
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'boolean',
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'🚨 hasNotes should be a boolean - use Boolean(notes) or !!notes',
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)
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assert.strictEqual(
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solution.hasNotes,
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false,
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'🚨 hasNotes should be false when notes is undefined',
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)
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})
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await test('canCheckout is exported', () => {
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assert.ok(
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'canCheckout' in solution,
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'🚨 Make sure you export "canCheckout" - add: export { ..., canCheckout, ... }',
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)
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})
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await test('canCheckout should be false', () => {
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assert.strictEqual(
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typeof solution.canCheckout,
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'boolean',
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'🚨 canCheckout should be a boolean',
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)
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assert.strictEqual(
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solution.canCheckout,
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false,
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'🚨 canCheckout should be false when terms are not accepted',
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)
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})
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await test('canCreateAccount is exported', () => {
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assert.ok(
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'canCreateAccount' in solution,
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'🚨 Make sure you export "canCreateAccount" - add: export { ..., canCreateAccount }',
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)
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})
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await test('canCreateAccount should be false', () => {
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assert.strictEqual(
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typeof solution.canCreateAccount,
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'boolean',
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'🚨 canCreateAccount should be a boolean',
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)
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assert.strictEqual(
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solution.canCreateAccount,
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false,
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'🚨 canCreateAccount should be false when password is empty',
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)
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})

‎exercises/03.primitive-types/06.solution.truthy-falsy/index.ts‎

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// Account and Checkout Status
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// Using truthy and falsy values to drive decisions
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const username = 'kent'
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const nickname = ''
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const age = 0
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const email = 'kent@epicweb.dev'
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const password = ''
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const notes = undefined
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const cartTotal = 42
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const hasAcceptedTerms = false
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const hasUsername = Boolean(username)
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const hasNickname = Boolean(nickname)
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const hasAge = Boolean(age)
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const hasNotes = Boolean(notes)
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const canCheckout = Boolean(cartTotal) && hasAcceptedTerms
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const canCreateAccount = hasUsername && Boolean(email) && Boolean(password)
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// ✅ Verification
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console.log('Has username:', hasUsername)
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console.log('Has nickname:', hasNickname)
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console.log('Has age:', hasAge)
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console.log('Has notes:', hasNotes)
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console.log('Can checkout:', canCheckout)
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console.log('Can create account:', canCreateAccount)
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export {
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hasUsername,
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hasNickname,
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hasAge,
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hasNotes,
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canCheckout,
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canCreateAccount,
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}

‎exercises/03.primitive-types/06.solution.truthy-falsy/package.json‎

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{
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"name": "exercises_03.primitive-types_06.solution.truthy-falsy",
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"type": "module",
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"scripts": {
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"start": "npx @kentcdodds/log-module ./index.ts",
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"start:watch": "npx @kentcdodds/log-module --watch ./index.ts",
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"test": "node --test index.test.ts",
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"test:watch": "node --watch --test index.test.ts"
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}
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}

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