letarray=[1,2,4,5];array.includes(2);// truearray.includes(3);// false

letarray=[1,3,5,7,9,11];array.includes(3,1);// true 1番目つまり最初から検索開始するarray.includes(5,4);// falsearray.includes(1,-1);// false 最後尾から検索開始するarray.includes(11,-3);// true

Math.pow(2,2);// 4Math.pow(2,3);// 8

2**2;// 42**3;// 8

2**2**2;// 16Math.pow(Math.pow(2,2),2);// 16

"hello".padStart(6);// " hello""hello".padEnd(6);// "hello "

"hi".padStart(10);// "        hi" 8文字埋められた"welcome".padStart(10);// "   welcome" 4文字埋められた

conststrings=["short","medium length","very long string"];constlongestString=strings.sort(str=>str.length).map(str=>str.length)[0];strings.forEach(str=>console.log(str.padStart(longestString)));// very long string//    medium length//            short

"hello".padEnd(13," Alberto");// "hello Alberto""1".padStart(3,0);// "001""99".padStart(3,0);// "099"

constfamily={father:"Jonathan Kent",mother:"Martha Kent",son:"Clark Kent",}

Object.keys(family);// ["father", "mother", "son"]family.father;// "Jonathan Kent"

Object.values(family);// ["Jonathan Kent", "Martha Kent", "Clark Kent"]Object.entries(family);// ["father", "Jonathan Kent"]// ["mother", "Martha Kent"]// ["son", "Clark Kent"]

constmyObj={name:"Alberto",age:25,greet(){console.log("hello");},}Object.getOwnPropertyDescriptors(myObj);// age:{value: 25, writable: true, enumerable: true, configurable: true}// greet:{value: ƒ, writable: true, enumerable: true, configurable: true}// name:{value: "Alberto", writable: true, enumerable: true, configurable: true}

// 昔constobject={prop1:"prop",prop2:"propop"}// 現在constobject={prop1:"prop",prop2:"propop",}

// カンマ入れないconstobject={prop1:"prop",prop2:"propop"}// 同僚が最終行をコピペしてプロパティを追加したconstobject={prop1:"prop",prop2:"propop"prop3:"propopop"}// 突然エラーが出るようになった

// SharedArrayBuffer作成constbuffer=newSharedArrayBuffer(16);constuint8=newUint8Array(buffer);// これに各計算するuint8[0]=10;console.log(Atomics.add(uint8,0,5));// 10console.log(uint8[0])// 15console.log(Atomics.load(uint8,0));// 15

// SharedArrayBuffer作成constbuffer=newSharedArrayBuffer(16);constuint8=newUint8Array(buffer);// これに各計算するuint8[0]=10;console.log(Atomics.sub(uint8,0,5));// 10console.log(uint8[0])// 5console.log(Atomics.store(uint8,0,3));// 3console.log(Atomics.load(uint8,0));// 3

// GitHubからユーザを取得fetch('api.github.com/user/AlbertoMontalesi').then(res=>{// 値をJSONで返すreturnres.json();}).then(res=>{// 全てが正常に動作したらここに来るconsole.log(res);}).catch(err=>{// エラーがあったらここに来るconsole.log(err);})

functionwalk(amount){returnnewPromise((resolve,reject)=>{if(amount<500){reject("the value is too small");}setTimeout(()=>resolve(`you walked for ${amount}ms`),amount);});}walk(1000).then(res=>{console.log(res);returnwalk(500);}).then(res=>{console.log(res);returnwalk(700);}).then(res=>{console.log(res);returnwalk(800);}).then(res=>{console.log(res);returnwalk(100);}).then(res=>{console.log(res);returnwalk(400);}).then(res=>{console.log(res);returnwalk(600);});// you walked for 1000ms// you walked for 500ms// you walked for 700ms// you walked for 800ms// uncaught exception: the value is too small

functionwalk(amount){returnnewPromise((resolve,reject)=>{if(amount<500){reject("the value is too small");}setTimeout(()=>resolve(`you walked for ${amount}ms`),amount);});}// asyncなfunctionを作成asyncfunctiongo(){// awaitがあれば終わるまで待つconstres=awaitwalk(500);console.log(res);constres2=awaitwalk(900);console.log(res2);constres3=awaitwalk(600);console.log(res3);constres4=awaitwalk(700);console.log(res4);constres5=awaitwalk(400);console.log(res5);console.log("finished");}go();// you walked for 500ms // you walked for 900ms // you walked for 600ms // you walked for 700ms // uncaught exception: the value is too small

// asyncではない関数functionfunc(){letpromise=Promise.resolve(1);letresult=awaitpromise;}func();// SyntaxError: await is only valid in async functions and async generators// トップレベルletresponse=Promise.resolve("hi");letresult=awaitresponse;// SyntaxError: await is only valid in async functions and async generators

asyncfunctionasyncFunc(){try{letresponse=awaitfetch('http:your-url');}catch(err){console.log(err);}}asyncFunc();// TypeError: failed to fetch

asyncfunctionasyncFunc(){letresponse=awaitfetch('http:your-url');}asyncFunc();// Uncaught (in promise) TypeError: Failed to fetchasyncFunc().catch(console.log);// TypeError: Failed to fetch

constveggie=["tomato","cucumber","beans"];constmeat=["pork","beef","chicken"];constmenu=[...veggie,"pasta",...meat];console.log(menu);// Array [ "tomato", "cucumber", "beans", "pasta", "pork", "beef", "chicken" ]

letmyObj={a:1,b:3,c:5,d:8,}// zは残り全部let{a,b,...z}=myObj;console.log(a);// 1console.log(b);// 3console.log(z);// {c: 5, d: 8}// スプレッド構文でクローンletclone={...myObj};console.log(clone);// {a: 1, b: 3, c: 5, d: 8}myObj.e=15;console.log(clone)// {a: 1, b: 3, c: 5, d: 8}console.log(myObj)// {a: 1, b: 3, c: 5, d: 8, e: 15}

constiterables=[1,2,3];asyncfunctiontest(){forawait(constvalueofiterables){console.log(value);}}test();// 1// 2// 3

constmyPromise=newPromise((resolve,reject)=>{resolve();})myPromise.then(()=>{console.log('still working');}).catch(()=>{console.log('there was an error');}).finally(()=>{console.log('Done!');})

constmyPromise=newPromise((resolve,reject)=>{resolve();})myPromise.then(()=>{console.log('still working');return'still working';}).finally(()=>{console.log('Done!');return'Done!';}).then(res=>{console.log(res);// still working})

/foo.bar/s.test('foo\nbar');// true

letre=/(?<year>\d{4})-(?<month>\d{2})-(?<day>\d{2})/u;letresult=re.exec('2015-01-02');// result.groups.year === '2015';// result.groups.month === '01';// result.groups.day === '02';// result[0] === '2015-01-02';// result[1] === '2015';// result[2] === '01';// result[3] === '02';let{groups:{one,two}}=/^(?<one>.*):(?<two>.*)$/u.exec('foo:bar');console.log(`one: ${one}, two: ${two}`);// one: foo, two: bar

constregexGreekSymbol=/\p{Script=Greek}/u;regexGreekSymbol.test('π');// true

constletters=['a','b',['c','d',['e','f']]];// デフォルトは1letters.flat();// ['a', 'b', 'c', 'd', ['e', 'f']]// 2段階letters.flat(2);// ['a', 'b', 'c', 'd', 'e', 'f']// 2段 = 1段 * 2letters.flat().flat();// ['a', 'b', 'c', 'd', 'e', 'f']// ネストがなくなるまで再帰的にフラット化letters.flat(Infinity)// ['a', 'b', 'c', 'd', 'e', 'f']

letgreeting=["Greetings from","","Vietnam"];// 普通のmapgreeting.map(x=>x.split(""));// ["Greetings", "from"]// ["", ""]// ["Vietnam"]// mapしてflatgreeting.flatMap(x=>x.split(""))// ["Greetings", "from", "", "", "Vietnam"]

constkeyValueArray=[['key1','value1'],['key2','value2']]constobj=Object.fromEntries(keyValueArray)// {key1: "value1", key2: "value2"}

letstr="    this string has a lot of whitespace   ";str.length;// 42str=str.trimStart();// "this string has a lot of whitespace   "str.length;// 38str=str.trimEnd();// "this string has a lot of whitespace"str.length;// 35

// Beforetry{...}catch(error){...}// ES2019try{...}catch{...}

functionsum(a,b){returna+b;}console.log(sum.toString());// function sum(a, b) {//    return a + b;//  }

functionsum(a,b){// perform a sumreturna+b;}console.log(sum.toString());// function sum(a, b) {//   // perform a sum//   return a + b;// }

constme=Symbol("Alberto");me.description;// "Alberto"me.toString()//  "Symbol(Alberto)"