functionbetween<T>(a1: T,a2: T,a3: T): boolean{returna2<=a1&&a1<=a3;}

functionbetween<T>(value: T,left: T,right: T): boolean{returnleft<=value&&value<=right;}

typeDtaRcrd102={genymdhms: Date;modymdhms: Date;pszqint: number;}

typeCustomer={generationTimestamp: Date;modificationTimestamp: Date;recordId: number;}

functiongetUserInfo(): User;functiongetUserDetails(): User;functiongetUserData(): User;

functiongetUser(): User;

// What the heck is 86400000 for?// 一体何が86400000なのか？setTimeout(restart,86400000);

// Declare them as capitalized named constants.// 定数の名前は大文字で宣言してください。constMILLISECONDS_IN_A_DAY=24*60*60*1000;setTimeout(restart,MILLISECONDS_IN_A_DAY);

declareconstusers: Map<string,User>;for(constkeyValueofusers){// iterate through users map// user map を反復処理する}

declareconstusers: Map<string,User>;for(const[id,user]ofusers){// iterate through users map// user map を反復処理する}

constu=getUser();consts=getSubscription();constt=charge(u,s);

constuser=getUser();constsubscription=getSubscription();consttransaction=charge(user,subscription);

typeCar={carMake: string;carModel: string;carColor: string;}functionprint(car: Car): void{console.log(`${car.carMake}${car.carModel} (${car.carColor})`);}

typeCar={make: string;model: string;color: string;}functionprint(car: Car): void{console.log(`${car.make}${car.model} (${car.color})`);}

functionloadPages(count?: number){constloadCount=count!==undefined ? count : 10;// ...}

functionloadPages(count: number=10){// ...}

constGENRE={ROMANTIC: 'romantic',DRAMA: 'drama',COMEDY: 'comedy',DOCUMENTARY: 'documentary',}projector.configureFilm(GENRE.COMEDY);classProjector{// delactation of Projector// 映写機を楽しむconfigureFilm(genre){switch(genre){caseGENRE.ROMANTIC: // some logic to be executed // 実行されるいくつかのロジック}}}

enumGENRE{ROMANTIC,DRAMA,COMEDY,DOCUMENTARY,}projector.configureFilm(GENRE.COMEDY);classProjector{// delactation of Projector// 映写機を楽しむconfigureFilm(genre){switch(genre){caseGENRE.ROMANTIC: // some logic to be executed // 実行されるいくつかのロジック}}}

functioncreateMenu(title: string,body: string,buttonText: string,cancellable: boolean){// ...}createMenu('Foo','Bar','Baz',true);

functioncreateMenu(options: {title: string,body: string,buttonText: string,cancellable: boolean}){// ...}createMenu({title: 'Foo',body: 'Bar',buttonText: 'Baz',cancellable: true});

typeMenuOptions={title: string,body: string,buttonText: string,cancellable: boolean};functioncreateMenu(options: MenuOptions){// ...}createMenu({title: 'Foo',body: 'Bar',buttonText: 'Baz',cancellable: true});

functionemailClients(clients: Client[]){clients.forEach((client)=>{constclientRecord=database.lookup(client);if(clientRecord.isActive()){email(client);}});}

functionemailClients(clients: Client[]){clients.filter(isActiveClient).forEach(email);}functionisActiveClient(client: Client){constclientRecord=database.lookup(client);returnclientRecord.isActive();}

functionaddToDate(date: Date,month: number): Date{// ...}constdate=newDate();// It's hard to tell from the function name what is added// 何が追加されたかを、関数名から予測することができません。addToDate(date,1);

functionaddMonthToDate(date: Date,month: number): Date{// ...}constdate=newDate();addMonthToDate(date,1);

functionparseCode(code: string){constREGEXES=[/* ... */];conststatements=code.split(' ');consttokens=[];REGEXES.forEach((regex)=>{statements.forEach((statement)=>{// ...});});constast=[];tokens.forEach((token)=>{// lex...});ast.forEach((node)=>{// parse...});}

constREGEXES=[/* ... */];functionparseCode(code: string){consttokens=tokenize(code);constsyntaxTree=parse(tokens);syntaxTree.forEach((node)=>{// parse...});}functiontokenize(code: string): Token[]{conststatements=code.split(' ');consttokens: Token[]=[];REGEXES.forEach((regex)=>{statements.forEach((statement)=>{tokens.push(/* ... */);});});returntokens;}functionparse(tokens: Token[]): SyntaxTree{constsyntaxTree: SyntaxTree[]=[];tokens.forEach((token)=>{syntaxTree.push(/* ... */);});returnsyntaxTree;}

functionshowDeveloperList(developers: Developer[]){developers.forEach((developer)=>{constexpectedSalary=developer.calculateExpectedSalary();constexperience=developer.getExperience();constgithubLink=developer.getGithubLink();constdata={ expectedSalary, experience, githubLink };render(data);});}functionshowManagerList(managers: Manager[]){managers.forEach((manager)=>{constexpectedSalary=manager.calculateExpectedSalary();constexperience=manager.getExperience();constportfolio=manager.getMBAProjects();constdata={ expectedSalary, experience, portfolio };render(data);});}

classDeveloper{// ...getExtraDetails(){return{githubLink: this.githubLink,}}}classManager{// ...getExtraDetails(){return{portfolio: this.portfolio,}}}functionshowEmployeeList(employee: Developer|Manager){employee.forEach((employee)=>{constexpectedSalary=employee.calculateExpectedSalary();constexperience=employee.getExperience();constextra=employee.getExtraDetails();constdata={ expectedSalary, experience, extra,};render(data);});}

typeMenuConfig={title?: string,body?: string,buttonText?: string,cancellable?: boolean};functioncreateMenu(config: MenuConfig){config.title=config.title||'Foo';config.body=config.body||'Bar';config.buttonText=config.buttonText||'Baz';config.cancellable=config.cancellable!==undefined ? config.cancellable : true;// ...}createMenu({body: 'Bar'});

typeMenuConfig={title?: string,body?: string,buttonText?: string,cancellable?: boolean};functioncreateMenu(config: MenuConfig){constmenuConfig=Object.assign({title: 'Foo',body: 'Bar',buttonText: 'Baz',cancellable: true},config);// ...}createMenu({body: 'Bar'});

typeMenuConfig={title?: string,body?: string,buttonText?: string,cancellable?: boolean};functioncreateMenu({ title ='Foo', body ='Bar', buttonText ='Baz', cancellable =true}: MenuConfig){// ...}createMenu({body: 'Bar'});

functioncreateFile(name: string,temp: boolean){if(temp){fs.create(`./temp/${name}`);}else{fs.create(name);}}

functioncreateTempFile(name: string){createFile(`./temp/${name}`);}functioncreateFile(name: string){fs.create(name);}

// Global variable referenced by following function.// 以下の関数で利用されるグローバル変数letname='Robert C. Martin';functiontoBase64(){name=btoa(name);}toBase64();// If we had another function that used this name, now it'd be a Base64 value// 変数 name を使用した別の関数がある場合は、その中身はBase64になります。console.log(name);// expected to print 'Robert C. Martin' but instead 'Um9iZXJ0IEMuIE1hcnRpbg=='// 'Robert C. Martin' と表示されるはずが、'Um9iZXJ0IEMuIE1hcnRpbg=='と表示されてしまう

constname='Robert C. Martin';functiontoBase64(text: string): string{returnbtoa(text);}constencodedName=toBase64(name);console.log(name);

functionaddItemToCart(cart: CartItem[],item: Item): void{cart.push({ item,date: Date.now()});};

functionaddItemToCart(cart: CartItem[],item: Item): CartItem[]{return[...cart,{ item,date: Date.now()}];};

declare global {interfaceArray<T>{diff(other: T[]): Array<T>;}}if(!Array.prototype.diff){Array.prototype.diff=function<T>(other: T[]): T[]{consthash=newSet(other);returnthis.filter(elem=>!hash.has(elem));};}

classMyArray<T>extendsArray<T>{diff(other: T[]): T[]{consthash=newSet(other);returnthis.filter(elem=>!hash.has(elem));};}

constcontributions=[{name: 'Uncle Bobby',linesOfCode: 500},{name: 'Suzie Q',linesOfCode: 1500},{name: 'Jimmy Gosling',linesOfCode: 150},{name: 'Gracie Hopper',linesOfCode: 1000}];lettotalOutput=0;for(leti=0;i<contributions.length;i++){totalOutput+=contributions[i].linesOfCode;}

constcontributions=[{name: 'Uncle Bobby',linesOfCode: 500},{name: 'Suzie Q',linesOfCode: 1500},{name: 'Jimmy Gosling',linesOfCode: 150},{name: 'Gracie Hopper',linesOfCode: 1000}];consttotalOutput=contributions.reduce((totalLines,output)=>totalLines+output.linesOfCode,0);

if(subscription.isTrial||account.balance>0){// ...}

functioncanActivateService(subscription: Subscription,account: Account){returnsubscription.isTrial||account.balance>0}if(canActivateService(subscription,account)){// ...}

functionisEmailNotUsed(email: string): boolean{// ...}if(isEmailNotUsed(email)){// ...}

functionisEmailUsed(email): boolean{// ...}if(!isEmailUsed(node)){// ...}

classAirplane{privatetype: string;// ...getCruisingAltitude(){switch(this.type){case'777': returnthis.getMaxAltitude()-this.getPassengerCount();case'Air Force One': returnthis.getMaxAltitude();case'Cessna': returnthis.getMaxAltitude()-this.getFuelExpenditure();default: thrownewError('Unknown airplane type.');}}privategetMaxAltitude(): number{// ...}}

abstractclassAirplane{protectedgetMaxAltitude(): number{// shared logic with subclasses ...}// ...}classBoeing777extendsAirplane{// ...getCruisingAltitude(){returnthis.getMaxAltitude()-this.getPassengerCount();}}classAirForceOneextendsAirplane{// ...getCruisingAltitude(){returnthis.getMaxAltitude();}}classCessnaextendsAirplane{// ...getCruisingAltitude(){returnthis.getMaxAltitude()-this.getFuelExpenditure();}}

functiontravelToTexas(vehicle: Bicycle|Car){if(vehicleinstanceofBicycle){vehicle.pedal(currentLocation,newLocation('texas'));}elseif(vehicleinstanceofCar){vehicle.drive(currentLocation,newLocation('texas'));}}

typeVehicle=Bicycle|Car;functiontravelToTexas(vehicle: Vehicle){vehicle.move(currentLocation,newLocation('texas'));}

// On old browsers, each iteration with uncached `list.length` would be costly// because of `list.length` recomputation. In modern browsers, this is optimized.// 古いブラウザは、キャッシュされていない `list.length` を使った繰り返しはコストがかかるでしょう// なぜなら、呼ばれるたびに `list.length` が再計算されるから。 モダンブラウザは最適化されているfor(leti=0,len=list.length;i<len;i++){// ...}

for(leti=0;i<list.length;i++){// ...}

functionoldRequestModule(url: string){// ...}functionrequestModule(url: string){// ...}constreq=requestModule;inventoryTracker('apples',req,'www.inventory-awesome.io');

functionrequestModule(url: string){// ...}constreq=requestModule;inventoryTracker('apples',req,'www.inventory-awesome.io');

functionfibonacci(n: number): number[]{if(n===1)return[0];if(n===2)return[0,1];constitems: number[]=[0,1];while(items.length<n){items.push(items[items.length-2]+items[items.length-1]);}returnitems;}functionprint(n: number){fibonacci(n).forEach(fib=>console.log(fib));}// Print first 10 Fibonacci numbers.// フィボナッチ数の最初の10個をprintするprint(10);

// Generates an infinite stream of Fibonacci numbers.// The generator doesn't keep the array of all numbers.// フィボナッチ数の無限のストリームを生成します// ジェネレータは全数の配列を保持しませんfunction*fibonacci(): IterableIterator<number>{let[a,b]=[0,1];while(true){yielda;[a,b]=[b,a+b];}}functionprint(n: number){leti=0;for(constfiboffibonacci()){if(i++===n)break;console.log(fib);}}// Print first 10 Fibonacci numbers.// フィボナッチ数の最初の10個をprintするprint(10);

importitiririfrom'itiriri';function*fibonacci(): IterableIterator<number>{let[a,b]=[0,1];while(true){yielda;[a,b]=[b,a+b];}}itiriri(fibonacci()).take(10).forEach(fib=>console.log(fib));

typeBankAccount={balance: number;// ...}constvalue=100;constaccount: BankAccount={balance: 0,// ...};if(value<0){thrownewError('Cannot set negative balance.');}account.balance=value;

classBankAccount{privateaccountBalance: number=0;getbalance(): number{returnthis.accountBalance;}setbalance(value: number){if(value<0){thrownewError('Cannot set negative balance.');}this.accountBalance=value;}// ...}// Now `BankAccount` encapsulates the validation logic.// If one day the specifications change, and we need extra validation rule,// we would have to alter only the `setter` implementation,// leaving all dependent code unchanged.// これで `BankAccount` はバリデーション処理をカプセル化しました。// ある日仕様が変更されて、追加のバリデーションが必要になった場合にも// `setter`の実装だけを変更すればよく// すべての依存したコードを変更する必要はありません。constaccount=newBankAccount();account.balance=100;

classCircle{radius: number;constructor(radius: number){this.radius=radius;}perimeter(){return2*Math.PI*this.radius;}surface(){returnMath.PI*this.radius*this.radius;}}

classCircle{constructor(privatereadonlyradius: number){}perimeter(){return2*Math.PI*this.radius;}surface(){returnMath.PI*this.radius*this.radius;}}

interfaceConfig{host: string;port: string;db: string;}

interfaceConfig{readonlyhost: string;readonlyport: string;readonlydb: string;}

constarray: number[]=[1,3,5];array=[];// errorarray.push(100);// array will updated

constarray: ReadonlyArray<number>=[1,3,5];array=[];// errorarray.push(100);// error

functionhoge(args: readonlystring[]){args.push(1);// error}

constconfig={hello: 'world'};config.hello='world';// value is changedconstarray=[1,3,5];array[0]=10;// value is changed// writable objects is returnedfunctionreadonlyData(value: number){return{ value };}constresult=readonlyData(100);result.value=200;// value is changed

// read-only objectconstconfig={hello: 'world'}asconst;config.hello='world';// error// read-only arrayconstarray=[1,3,5]asconst;array[0]=10;// error// You can return read-only objectsfunctionreadonlyData(value: number){return{ value }asconst;}constresult=readonlyData(100);result.value=200;// error

interfaceEmailConfig{// ...}interfaceDbConfig{// ...}interfaceConfig{// ...}//...typeShape={// ...}

typeEmailConfig={// ...}typeDbConfig={// ...}typeConfig=EmailConfig|DbConfig;// ...interfaceShape{// ...}classCircleimplementsShape{// ...}classSquareimplementsShape{// ...}

classDashboard{getLanguage(): string{/* ... */}setLanguage(language: string): void{/* ... */}showProgress(): void{/* ... */}hideProgress(): void{/* ... */}isDirty(): boolean{/* ... */}disable(): void{/* ... */}enable(): void{/* ... */}addSubscription(subscription: Subscription): void{/* ... */}removeSubscription(subscription: Subscription): void{/* ... */}addUser(user: User): void{/* ... */}removeUser(user: User): void{/* ... */}goToHomePage(): void{/* ... */}updateProfile(details: UserDetails): void{/* ... */}getVersion(): string{/* ... */}// ...}

classDashboard{disable(): void{/* ... */}enable(): void{/* ... */}getVersion(): string{/* ... */}}// split the responsibilities by moving the remaining methods to other classes// 他のクラスにメソッドを移動して責任を分割する// ...

classUserManager{// Bad: each private variable is used by one or another group of methods.// It makes clear evidence that the class is holding more than a single responsibility.// If I need only to create the service to get the transactions for a user,// I'm still forced to pass and instance of `emailSender`.// 悪い: 各プライベート変数は、メソッドの1つまたは別のグループによって使用されます。// それは、クラスが1つ以上の責任を保持しているという明確な証拠を表しています。// ユーザーのトランザクションを取得するためだけにサービスを作成する必要がある場合は、// `emailSender` のインスタンスを渡すことを余儀なくされています。constructor(privatereadonlydb: Database,privatereadonlyemailSender: EmailSender){}asyncgetUser(id: number): Promise<User>{returnawaitdb.users.findOne({ id });}asyncgetTransactions(userId: number): Promise<Transaction[]>{returnawaitdb.transactions.find({ userId });}asyncsendGreeting(): Promise<void>{awaitemailSender.send('Welcome!');}asyncsendNotification(text: string): Promise<void>{awaitemailSender.send(text);}asyncsendNewsletter(): Promise<void>{// ...}}

classUserService{constructor(privatereadonlydb: Database){}asyncgetUser(id: number): Promise<User>{returnawaitthis.db.users.findOne({ id });}asyncgetTransactions(userId: number): Promise<Transaction[]>{returnawaitthis.db.transactions.find({ userId });}}classUserNotifier{constructor(privatereadonlyemailSender: EmailSender){}asyncsendGreeting(): Promise<void>{awaitthis.emailSender.send('Welcome!');}asyncsendNotification(text: string): Promise<void>{awaitthis.emailSender.send(text);}asyncsendNewsletter(): Promise<void>{// ...}}

classEmployee{constructor(privatereadonlyname: string,privatereadonlyemail: string){}// ...}// Bad because Employees "have" tax data. EmployeeTaxData is not a type of Employee// よくない。なぜなら、従業員(Employee)は税情報を持っている。しかし、従業員税情報(EmployeeTaxData)は従業員ではないclassEmployeeTaxDataextendsEmployee{constructor(name: string,email: string,privatereadonlyssn: string,privatereadonlysalary: number){super(name,email);}// ...}

classEmployee{privatetaxData: EmployeeTaxData;constructor(privatereadonlyname: string,privatereadonlyemail: string){}setTaxData(ssn: string,salary: number): Employee{this.taxData=newEmployeeTaxData(ssn,salary);returnthis;}// ...}classEmployeeTaxData{constructor(publicreadonlyssn: string,publicreadonlysalary: number){}// ...}

classQueryBuilder{privatecollection: string;privatepageNumber: number=1;privateitemsPerPage: number=100;privateorderByFields: string[]=[];from(collection: string): void{this.collection=collection;}page(number: number,itemsPerPage: number=100): void{this.pageNumber=number;this.itemsPerPage=itemsPerPage;}orderBy(...fields: string[]): void{this.orderByFields=fields;}build(): Query{// ...}}// ...constqueryBuilder=newQueryBuilder();queryBuilder.from('users');queryBuilder.page(1,100);queryBuilder.orderBy('firstName','lastName');constquery=queryBuilder.build();

classQueryBuilder{privatecollection: string;privatepageNumber: number=1;privateitemsPerPage: number=100;privateorderByFields: string[]=[];from(collection: string): this {this.collection=collection;returnthis;}page(number: number,itemsPerPage: number=100): this {this.pageNumber=number;this.itemsPerPage=itemsPerPage;returnthis;}orderBy(...fields: string[]): this {this.orderByFields=fields;returnthis;}build(): Query{// ...}}// ...constquery=newQueryBuilder().from('users').page(1,100).orderBy('firstName','lastName').build();

classUserSettings{constructor(privatereadonlyuser: User){}changeSettings(settings: UserSettings){if(this.verifyCredentials()){// ...}}verifyCredentials(){// ...}}

classUserAuth{constructor(privatereadonlyuser: User){}verifyCredentials(){// ...}}classUserSettings{privatereadonlyauth: UserAuth;constructor(privatereadonlyuser: User){this.auth=newUserAuth(user);}changeSettings(settings: UserSettings){if(this.auth.verifyCredentials()){// ...}}}

classAjaxAdapterextendsAdapter{constructor(){super();}// ...}classNodeAdapterextendsAdapter{constructor(){super();}// ...}classHttpRequester{constructor(privatereadonlyadapter: Adapter){}asyncfetch<T>(url: string): Promise<T>{if(this.adapterinstanceofAjaxAdapter){constresponse=awaitmakeAjaxCall<T>(url);// transform response and return}elseif(this.adapterinstanceofNodeAdapter){constresponse=awaitmakeHttpCall<T>(url);// transform response and return}}}functionmakeAjaxCall<T>(url: string): Promise<T>{// request and return promise}functionmakeHttpCall<T>(url: string): Promise<T>{// request and return promise}

abstractclassAdapter{abstractasyncrequest<T>(url: string): Promise<T>;// code shared to subclasses ...}classAjaxAdapterextendsAdapter{constructor(){super();}asyncrequest<T>(url: string): Promise<T>{// request and return promise}// ...}classNodeAdapterextendsAdapter{constructor(){super();}asyncrequest<T>(url: string): Promise<T>{// request and return promise}// ...}classHttpRequester{constructor(privatereadonlyadapter: Adapter){}asyncfetch<T>(url: string): Promise<T>{constresponse=awaitthis.adapter.request<T>(url);// transform response and return}}

classRectangle{constructor(protectedwidth: number=0,protectedheight: number=0){}setColor(color: string): this {// ...}render(area: number){// ...}setWidth(width: number): this {this.width=width;returnthis;}setHeight(height: number): this {this.height=height;returnthis;}getArea(): number{returnthis.width*this.height;}}classSquareextendsRectangle{setWidth(width: number): this {this.width=width;this.height=width;returnthis;}setHeight(height: number): this {this.width=height;this.height=height;returnthis;}}functionrenderLargeRectangles(rectangles: Rectangle[]){rectangles.forEach((rectangle)=>{constarea=rectangle.setWidth(4).setHeight(5).getArea();// BAD: Returns 25 for Square. Should be 20.rectangle.render(area);});}constrectangles=[newRectangle(),newRectangle(),newSquare()];renderLargeRectangles(rectangles);

abstractclassShape{setColor(color: string): this {// ...}render(area: number){// ...}abstractgetArea(): number;}classRectangleextendsShape{constructor(privatereadonlywidth=0,privatereadonlyheight=0){super();}getArea(): number{returnthis.width*this.height;}}classSquareextendsShape{constructor(privatereadonlylength: number){super();}getArea(): number{returnthis.length*this.length;}}functionrenderLargeShapes(shapes: Shape[]){shapes.forEach((shape)=>{constarea=shape.getArea();shape.render(area);});}constshapes=[newRectangle(4,5),newRectangle(4,5),newSquare(5)];renderLargeShapes(shapes);

interfaceSmartPrinter{print();fax();scan();}classAllInOnePrinterimplementsSmartPrinter{print(){// ...}fax(){// ...}scan(){// ...}}classEconomicPrinterimplementsSmartPrinter{print(){// ...}fax(){thrownewError('Fax not supported.');}scan(){thrownewError('Scan not supported.');}}

interfacePrinter{print();}interfaceFax{fax();}interfaceScanner{scan();}classAllInOnePrinterimplementsPrinter,Fax,Scanner{print(){// ...}fax(){// ...}scan(){// ...}}classEconomicPrinterimplementsPrinter{print(){// ...}}

import{readFileasreadFileCb}from'fs';import{promisify}from'util';constreadFile=promisify(readFileCb);typeReportData={// ..}classXmlFormatter{parse<T>(content: string): T{// Converts an XML string to an object T// XML文字列をTオブジェクトに変換します。}}classReportReader{// BAD: We have created a dependency on a specific request implementation.// We should just have ReportReader depend on a parse method: `parse`// 悪い：特定のリクエストに依存する実装を作りました。// ReportReaderを parseメソッドに依存させています：`parse`privatereadonlyformatter=newXmlFormatter();asyncread(path: string): Promise<ReportData>{consttext=awaitreadFile(path,'UTF8');returnthis.formatter.parse<ReportData>(text);}}// ...constreader=newReportReader();awaitreport=awaitreader.read('report.xml');

import{readFileasreadFileCb}from'fs';import{promisify}from'util';constreadFile=promisify(readFileCb);typeReportData={// ..}interfaceFormatter{parse<T>(content: string): T;}classXmlFormatterimplementsFormatter{parse<T>(content: string): T{// Converts an XML string to an object T// XML文字列をTオブジェクトに変換します。}}classJsonFormatterimplementsFormatter{parse<T>(content: string): T{// Converts a JSON string to an object T// json文字列をTオブジェクトに変換します。}}classReportReader{constructor(privatereadonlyformatter: Formatter){}asyncread(path: string): Promise<ReportData>{consttext=awaitreadFile(path,'UTF8');returnthis.formatter.parse<ReportData>(text);}}// ...constreader=newReportReader(newXmlFormatter());awaitreport=awaitreader.read('report.xml');// or if we had to read a json report// JSONレポートを読む場合constreader=newReportReader(newJsonFormatter());awaitreport=awaitreader.read('report.json');

import{assert}from'chai';describe('AwesomeDate',()=>{it('handles date boundaries',()=>{letdate: AwesomeDate;date=newAwesomeDate('1/1/2015');assert.equal('1/31/2015',date.addDays(30));date=newAwesomeDate('2/1/2016');assert.equal('2/29/2016',date.addDays(28));date=newAwesomeDate('2/1/2015');assert.equal('3/1/2015',date.addDays(28));});});

import{assert}from'chai';describe('AwesomeDate',()=>{it('handles 30-day months',()=>{constdate=newAwesomeDate('1/1/2015');assert.equal('1/31/2015',date.addDays(30));});it('handles leap year',()=>{constdate=newAwesomeDate('2/1/2016');assert.equal('2/29/2016',date.addDays(28));});it('handles non-leap year',()=>{constdate=newAwesomeDate('2/1/2015');assert.equal('3/1/2015',date.addDays(28));});});

describe('Calendar',()=>{it('2/29/2020',()=>{// ...});it('throws',()=>{// ...});});

describe('Calendar',()=>{it('should handle leap year',()=>{// ...});it('should throw when format is invalid',()=>{// ...});});

import{get}from'request';import{writeFile}from'fs';functiondownloadPage(url: string,saveTo: string,callback: (error: Error,content?: string)=>void){get(url,(error,response)=>{if(error){callback(error);}else{writeFile(saveTo,response.body,(error)=>{if(error){callback(error);}else{callback(null,response.body);}});}});}downloadPage('https://en.wikipedia.org/wiki/Robert_Cecil_Martin','article.html',(error,content)=>{if(error){console.error(error);}else{console.log(content);}});

import{get}from'request';import{writeFile}from'fs';import{promisify}from'util';constwrite=promisify(writeFile);functiondownloadPage(url: string,saveTo: string): Promise<string>{returnget(url).then(response=>write(saveTo,response));}downloadPage('https://en.wikipedia.org/wiki/Robert_Cecil_Martin','article.html').then(content=>console.log(content)).catch(error=>console.error(error));

import{get}from'request';import{writeFile}from'fs';import{promisify}from'util';constwrite=util.promisify(writeFile);functiondownloadPage(url: string,saveTo: string): Promise<string>{returnget(url).then(response=>write(saveTo,response));}downloadPage('https://en.wikipedia.org/wiki/Robert_Cecil_Martin','article.html').then(content=>console.log(content)).catch(error=>console.error(error));

import{get}from'request';import{writeFile}from'fs';import{promisify}from'util';constwrite=promisify(writeFile);asyncfunctiondownloadPage(url: string,saveTo: string): Promise<string>{constresponse=awaitget(url);awaitwrite(saveTo,response);returnresponse;}// somewhere in an async functiontry{constcontent=awaitdownloadPage('https://en.wikipedia.org/wiki/Robert_Cecil_Martin','article.html');console.log(content);}catch(error){console.error(error);}

functioncalculateTotal(items: Item[]): number{throw'Not implemented.';}functionget(): Promise<Item[]>{returnPromise.reject('Not implemented.');}

functioncalculateTotal(items: Item[]): number{thrownewError('Not implemented.');}functionget(): Promise<Item[]>{returnPromise.reject(newError('Not implemented.'));}// or equivalent to:asyncfunctionget(): Promise<Item[]>{thrownewError('Not implemented.');}

typeResult<R>={isError: false,value: R};typeFailure<E>={isError: true,error: E};typeFailable<R,E>=Result<R>|Failure<E>;functioncalculateTotal(items: Item[]): Failable<number,'empty'>{if(items.length===0){return{isError: true,error: 'empty'};}// ...return{isError: false,value: 42};}

try{functionThatMightThrow();}catch(error){console.log(error);}// or even worsetry{functionThatMightThrow();}catch(error){// ignore error}

import{logger}from'./logging'try{functionThatMightThrow();}catch(error){logger.log(error);}

getUser().then((user: User)=>{returnsendEmail(user.email,'Welcome!');}).catch((error)=>{console.log(error);});

import{logger}from'./logging'getUser().then((user: User)=>{returnsendEmail(user.email,'Welcome!');}).catch((error)=>{logger.log(error);});// or using the async/await syntax:// もしくは async/await 構文を使うtry{constuser=awaitgetUser();awaitsendEmail(user.email,'Welcome!');}catch(error){logger.log(error);}

constDAYS_IN_WEEK=7;constdaysInMonth=30;constsongs=['Back In Black','Stairway to Heaven','Hey Jude'];constArtists=['ACDC','Led Zeppelin','The Beatles'];functioneraseDatabase(){}functionrestore_database(){}typeanimal={/* ... */}typeContainer={/* ... */}

constDAYS_IN_WEEK=7;constDAYS_IN_MONTH=30;constSONGS=['Back In Black','Stairway to Heaven','Hey Jude'];constARTISTS=['ACDC','Led Zeppelin','The Beatles'];functioneraseDatabase(){}functionrestoreDatabase(){}typeAnimal={/* ... */}typeContainer={/* ... */}