constgetPermutation=(types,r)=>{constresult=[];// r が 1 の場合if(r===1){for(leti=0;i<types.length;i++){result[i]=[types[i]];}returnresult;}// r が 2以上の場合for(leti=0;i<types.length;i++){constparts=types.slice(0);parts.splice(i,1)[0];constrow=getPermutation(parts,r-1);for(letj=0;j<row.length;j++){result.push([types[i]].concat(row[j]));}}returnresult;};
Rails.application.config.content_security_policy_nonce_generator=->(request)do# use the same csp nonce for turbolinks requestsifrequest.env['HTTP_TURBOLINKS_REFERRER'].present?request.env['HTTP_X_TURBOLINKS_NONCE']elseSecureRandom.base64(16)end
createAlgoliaIndex=function(appId,apiKey,indexName){consturl=`https://${appId}-dsn.algolia.net/1/indexes/${indexName}/settings`constheaders={'X-Algolia-API-Key':apiKey,'X-Algolia-Application-Id':appId}letreq=newRequest(url,{method:'PUT',body:JSON.stringify({searchableAttributes:["title","authors","purchaseDate"],customRanking:["desc(purchaseDate)"],attributesForFaceting:["searchable(authors)"]}),headers:headers})fetch(req).then(response=>{if(response.status===200){console.log(response.json());}else{thrownewError('Something went wrong on api server!'+response.json());}}).then(response=>{console.debug(response);}).catch(error=>{console.error(error);});}createAlgoliaIndex(appId,apiKey,indexName)
以下のコードを実行しkindle libraryのデータをAlogliaに登録する
sendKindleToAlgolia=function(appId,apiKey,indexName){letdb=openDatabase('K4W','3','thedatabase',1024*1024);consturl=`https://${appId}-dsn.algolia.net/1/indexes/${indexName}/batch`constheaders={'X-Algolia-API-Key':apiKey,'X-Algolia-Application-Id':appId}db.transaction(function(tx){tx.executeSql('SELECT * FROM bookdata order by title;',[],function(tx,results){constlen=results.rows.length;letbatch=[]for(i=0;i<len;i++){letresult=results.rows.item(i);letasin=result.asin;lettitle=result.title;letauthors=JSON.parse(result.authors);letpurchaseDate=newDate(result.purchaseDate).toLocaleDateString();letproductUrl=`https://www.amazon.co.jp/dp/${asin}`letproductImageUrl=`https://images-na.ssl-images-amazon.com/images/P/${asin}.09.MZZZZZZZ.jpg`// Remove double quotes and CRLF from titletitle=title.replace(/"/g,'');title=title.replace(/\n|\r\n|\r/g,'');// Add record to batchletrecord={asin:asin,title:title,authors:authors,purchaseDate:purchaseDate,productUrl:productUrl,productImageUrl:productImageUrl}batch.push({action:'addObject',body:record})}letreq=newRequest(url,{method:'POST',body:JSON.stringify({requests:batch}),headers:headers})fetch(req).then(response=>{if(response.status===200){console.log(response.json());}else{thrownewError('Something went wrong on api server!'+response.json());}}).then(response=>{console.debug(response);}).catch(error=>{console.error(error);});});});};sendKindleToAlgolia(appId,apiKey,indexName);
constobj={aaa:{}}obj.aaa.bbb// undefinedobj.aaa.bbb?.ccc.ddd// undefined (no error)obj.aaa// {}obj.aaa?.bbb// undefinedobj.aaa?.bbb.ccc// Uncaught TypeError: // Cannot read property 'ccc' of undefined
obj.aaa?.bbb.ccc で、 aaa?. は undefined について未判定。
.bbb の時点で ?. 未判定のため、後続の .ccc が undefined 判定される。
.ccc は undefined なのでエラーになる。
Nullish ?? Coalescing
?? の第二項の式は、第一項が undefined か null ではない場合には評価されない。
第二項は実行されない。
functionfunc(){console.log('Done second operand.')return2}1??func()// 1 (no message)false??func()// false (no message)''??func()// '' (no message)NaN??func()// NaN (no message)undefined??func()// 2 (message: Done second operand.)null??func()// 2 (message: Done second operand.)
functionfunc(){console.log('Done second operand.')return2}1??func()// 1 (no message)false??func()// false (no message)''??func()// '' (no message)NaN??func()// NaN (no message)undefined??func()// 2 (message: Done second operand.)null??func()// 2 (message: Done second operand.)
importReactfrom'react';importReactDOMfrom'react-dom';import'./index.css';importMoneyBookfrom'./App';import*asserviceWorkerfrom'./serviceWorker';ReactDOM.render(<MoneyBook/>,document.getElementById('root'));// If you want your app to work offline and load faster, you can change// unregister() to register() below. Note this comes with some pitfalls.// Learn more about service workers: https://bit.ly/CRA-PWAserviceWorker.unregister();
