投稿時間:2022-09-28 06:22:08 RSSフィード2022-09-28 06:00 分まとめ(24件)

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IT	ITmedia 総合記事一覧	[ITmedia ビジネスオンライン] 衝撃の「子どもIC運賃50円」開始から半年　小田急電鉄に手応えを聞いた	https://www.itmedia.co.jp/business/articles/2209/28/news047.html	itmedia	2022-09-28 05:30:00
海外TECH	Ars Technica	Apple no longer replacing entire iPad mini 6 just to swap the battery	https://arstechnica.com/?p=1884794	battery	2022-09-27 20:26:23
海外TECH	MakeUseOf	Is Virtual Photography Real Photography?	https://www.makeuseof.com/is-virtual-photography-real-photography/	world	2022-09-27 20:30:14
海外TECH	MakeUseOf	How to Use MAXIFS and MINIFS Functions in Excel	https://www.makeuseof.com/use-maxifs-minifs-functions-excel/	minimum	2022-09-27 20:15:14
海外TECH	DEV Community	A Complete Guide to Javascript Maps	https://dev.to/smpnjn/a-complete-guide-to-javascript-maps-1162	A Complete Guide to Javascript MapsYou re probably familiar with Javascript Objects but did you know there is another way to create sets of data in Javascript known as Maps You might be using Javascript plain old objects right now when a map may be a better solution to your problem Javascript maps differ in a few major ways to objects Although typeof new Map returns object don t let that fool you Here are some of the major differences from objects Does not contain any keys by default unlike objects which contain a prototype object They are guaranteed to be ordered by the order they were inserted Objects are like this too these days but they don t carry the same guarantee The keys of a map can be anything including a function or even an object Whereas in Javascript it must be a string or symbol They have better performance than objects on tasks which require rapid or frequent removal or addition of data They are iterable by default unlike objects Given that maps have so many benefits let s take a look at how they work The Basics of how Javascript Maps workAny map in Javascript is initiated using the new Map constructor For example let s create a map called myFirstMap let myFirstMap new Map The difference is to set get or delete keys from a map you have to use specific methods that come along with Map So to set a new value of someValue with the key firstKey I can run the following method let myFirstMap new Map myFirstMap set firstKey someValue Deleting an item in a Javascript MapIf we then wanted to delete a key in a Javascript map we have to call the delete method let myFirstMap new Map myFirstMap set firstKey someValue myFirstMap delete firstKey You can also delete the entire map altogether leaving no items in it using clear let myFirstMap new Map myFirstMap set firstKey someValue myFirstMap clear console log myFirstMap Returns Map Getting a key in a Javascript MapSimilar in usage to the other methods to get the value of firstKey we have to use get let myFirstMap new Map myFirstMap set firstKey someValue myFirstMap get firstKey someValue Checking if a key exists in a Javascript MapJavascript Maps also have a method called has if we want to check if a map has a certain key let myFirstMap new Map myFirstMap set firstKey someValue myFirstMap has firstKey true Warning don t use typical Object properties with MapsJavascript is full of quirks and maps are no different Weirdly maps can also support object notation For example this seems to work let myFirstMap new Map myFirstMap firstKey someValue console log myFirstMap Map firstKey someValue However you should not do this This is not creating new entries in the map itself you re simply creating an object So you ll lose all the benefits of Javascript maps Telling how big a Javascript Map isOne other useful thing where maps are a little easier to use than objects is finding out how many keys are in a map For this we can use the size method which returns the number of keys let myFirstMap new Map myFirstMap set firstKey someValue myFirstMap size For objects we typically use a mixture of Object keys and length to find out the size of an object let myObj name John let sizeOfObj Object keys myObj length Using Maps with non string keysAs I mentioned Javascript Maps allow non conventional keys like functions and objects whereas objects only allow strings and symbols For example this is valid in a map let myFirstMap new Map let myFunction function return someReturn myFirstMap set myFunction value Map keys are based on reference not value That means although the following will work let myFirstMap new Map let myFunction function return someReturn myFirstMap set myFunction value myFirstMap get myFunction Returns someReturn This will not let myFirstMap new Map let myFunction function return someReturn myFirstMap set myFunction value myFirstMap get function return someReturn Returns undefinedmyFirstMap get someReturn Returns undefinedThat s because although function return someReturn and myFunction are the same in value they are not the same in terms of where they are stored in system memory So they are not exactly equivalent Similarly maps do not work on return value so myFirstMap get someReturn also returns undefined The same example works for objects with similar results let myFirstMap new Map let myObject someKey someValue myFirstMap set myObject value myFirstMap get someKey someValue Returns undefinedmyFirstMap get myObject Returns value Merging Javascript MapsIf you have multiple maps you want to merge into one you can merge them in the same way you merge objects with the spread syntax For example here I merge myFirstMap and mySecondMap into myNewMap using the spread syntax let myFirstMap new Map myFirstMap set some value let mySecondMap new Map mySecondMap set someOther value let myNewMap new Map myFirstMap mySecondMap console log myNewMap Map some value someOther value Iterating on a MapAs mentioned maps are iterable by default If we want to iterate over objects we usually have to use a function like Object keys Ultimately this means we can use forEach on any map like so let myFirstMap new Map myFirstMap set some value myFirstMap set someOther value myFirstMap forEach function value key map value gt the value of that key in the map key gt the key for this item in the map map gt the entire map console log value key map Iterating on a Javascript Map using forYou can also iterate on a map using for let of If you do that each item is returned as an array of the key and value For example let myFirstMap new Map myFirstMap set some value for let x of myFirstMap Returns some value console log x Iterating over values or keys in Javascript MapsAnother cool way we can iterate over values or keys in Javascript is to use the values or entries methods These return a new iterator for the values and items in a map respectively That means we can access the next key or value using next functions just like in generator functions For example let s look at how entries works let myFirstMap new Map myFirstMap set some value myFirstMap set someOther value myFirstMap set aFinal value let allKeys myFirstMap entries console log allKeys Returns MapIterator objectconsole log allKeys next Returns value some value done false console log allKeys next value Returns some value Our return from allKeys next is an object The value in this object is some value an array of the first item in our map We can keep running next to get the following items in the map Pretty cool We can do the same thing again with just values let myFirstMap new Map myFirstMap set some value myFirstMap set someOther value myFirstMap set aFinal value let allValues myFirstMap values console log allValues Returns MapIterator objectconsole log allValues next Returns value value done false console log allValues next value Returns value Iterators like this prove useful in some specific situations and can be a cool way to iterate through all the data in your Map Serialization of Maps in JavascriptOne of the drawbacks for some people which maps have is that they cannot be easily serialized with JSON parse and JSON stringify Trying to do so results in an empty object and this kind of makes sense since the object of a Map is empty if we only populate it with entries let myFirstMap new Map myFirstMap set some value myFirstMap set someOther value myFirstMap set aFinal value Returns console log JSON stringify myFirstMap The only realistic way to serialize a Map is to convert it to an object or array which simply means you ll have to maintain some separate helper functions to do this task for you should you use Maps For example we can use Array from to convert our Map to an array and then use JSON stringify to serialize it let myFirstMap new Map myFirstMap set some value myFirstMap set someOther value myFirstMap set aFinal value let arrayMap Array from myFirstMap Returns some value someOther value aFinal value console log JSON stringify arrayMap Then if we want to turn it back into a map we have to use JSON parse in conjunction with new Map let myFirstMap new Map myFirstMap set some value myFirstMap set someOther value myFirstMap set aFinal value Turn our map into an arraylet arrayMap Array from myFirstMap The JSON stringed version of our map let stringifiedMap JSON stringify arrayMap Use new Map JSON parse to turn our stringed map into a map again let getMap new Map JSON parse stringifiedMap Returns Map   some gt value someOther gt value aFinal gt value console log getMap ConclusionJavascript Maps are a great way to store data when you don t need all the flexibility of objects and things like the order of your data are incredibly important They also prove more performant than objects in situations requiring frequent addition and removal of items In this guide we ve covered everything you need to know about Maps but if you want to learn more about Javascript click here Hope you ve enjoyed this one have a great day	2022-09-27 20:30:07
ニュース	BBC News - Home	Royal Mail workers to hold 19 days of strike action	https://www.bbc.co.uk/news/business-63055394?at_medium=RSS&at_campaign=KARANGA	cyber	2022-09-27 20:52:13
ニュース	BBC News - Home	Home Secretary criticises Sussex force for 'policing pronouns'	https://www.bbc.co.uk/news/uk-england-sussex-63055024?at_medium=RSS&at_campaign=KARANGA	child	2022-09-27 20:47:55
ニュース	BBC News - Home	Peaky Blinders creator Steven Knight hints at new series	https://www.bbc.co.uk/news/uk-england-birmingham-63054433?at_medium=RSS&at_campaign=KARANGA	writers	2022-09-27 20:43:46
ニュース	BBC News - Home	Mass shootings: What are the warning signs and could they help prevent another Parkland?	https://www.bbc.co.uk/news/world-us-canada-62683094?at_medium=RSS&at_campaign=KARANGA	experts	2022-09-27 20:11:31
ニュース	BBC News - Home	Ukraine 0-0 Scotland: Steve Clarke's side earn Nations League promotion	https://www.bbc.co.uk/sport/football/62959155?at_medium=RSS&at_campaign=KARANGA	Ukraine Scotland Steve Clarke x s side earn Nations League promotionA depleted Scotland earn promotion to the top tier of the Nations League after a defensively disciplined and brave display clinches the point they needed against Ukraine	2022-09-27 20:38:44
ニュース	BBC News - Home	Nations League: NI avoid relegation as dismal campaign ends with defeat in Greece	https://www.bbc.co.uk/sport/football/62964258?at_medium=RSS&at_campaign=KARANGA	Nations League NI avoid relegation as dismal campaign ends with defeat in GreeceNorthern Ireland managed to retain their Nations League third tier status despite a dismal campaign ending in disappointing fashion with a defeat by Greece in Athens	2022-09-27 20:46:04
ニュース	BBC News - Home	Republic of Ireland 3-2 Armenia: Irish edge five-goal thriller to avoid Nations League drop	https://www.bbc.co.uk/sport/football/63034146?at_medium=RSS&at_campaign=KARANGA	Republic of Ireland Armenia Irish edge five goal thriller to avoid Nations League dropThe Republic of Ireland survive a major scare as they recover from squandering a two goal lead to beat Armenia in a chaotic Nations League game	2022-09-27 20:48:56
ニュース	BBC News - Home	Mortgage rates: 'If we can't afford higher payments, we lose our home'	https://www.bbc.co.uk/news/business-63046919?at_medium=RSS&at_campaign=KARANGA	interest	2022-09-27 20:39:24
ビジネス	ダイヤモンド・オンライン - 新着記事	電気＆ガス代「月1.4万円」もの差！編集部の前エネルギー担当記者が実践するガチ節約術 - 有料記事限定公開	https://diamond.jp/articles/-/310049	有効活用	2022-09-28 05:25:00
ビジネス	ダイヤモンド・オンライン - 新着記事	京セラ会長が悩んだ偉大すぎる創業者の影響力、「“脱・稲盛”を果たせたのはわずか5年前」 - 京都企業の血脈	https://diamond.jp/articles/-/310266	京セラ会長が悩んだ偉大すぎる創業者の影響力、「“脱・稲盛を果たせたのはわずか年前」京都企業の血脈京セラ創業者であり「経営の神様」と評される稲盛和夫氏が月日に死去した。	2022-09-28 05:20:00
ビジネス	ダイヤモンド・オンライン - 新着記事	住宅地の地価31年ぶり上昇、需要増だけではない「意外な理由」とは？エリア格差も拡大 - Diamond Premium News	https://diamond.jp/articles/-/310395	diamondpremiumnews	2022-09-28 05:17:00
ビジネス	ダイヤモンド・オンライン - 新着記事	日本電産・島津・オムロン首脳が集う「京都31社会」の正体、三菱UFJ銀が祇園のお茶屋で主催 - 京都企業の血脈	https://diamond.jp/articles/-/310265		2022-09-28 05:15:00
ビジネス	ダイヤモンド・オンライン - 新着記事	アサヒとダイドーの業務提携で号砲、中堅飲料メーカーの「自販機撤退戦」始まる - Diamond Premium News	https://diamond.jp/articles/-/310370	diamondpremiumnews	2022-09-28 05:10:00
ビジネス	ダイヤモンド・オンライン - 新着記事	関電・中部電・九電・中国電がカルテルで「巨額特損」危機！課徴金を免れそうな1社とは？ - 電力崩壊 業界新秩序	https://diamond.jp/articles/-/310048	特別損失	2022-09-28 05:05:00
ビジネス	電通報 | 広告業界動向とマーケティングのコラム・ニュース	広告は、“個人の想い”を伝える新たな表現の場になれる	https://dentsu-ho.com/articles/8339	mission	2022-09-28 06:00:00
ビジネス	電通報 | 広告業界動向とマーケティングのコラム・ニュース	なぜ、学問は必要なのか？	https://dentsu-ho.com/articles/8338	佐藤春夫	2022-09-28 06:00:00
北海道	北海道新聞	米、ロシア人亡命を歓迎　動員令で出国相次ぐ	https://www.hokkaido-np.co.jp/article/737149/	歓迎	2022-09-28 05:06:00
ビジネス	東洋経済オンライン	激増する｢不起訴の理由が不明｣記事が大問題な訳 凶悪犯罪でも真相が水面下に潜ってしまう | 災害･事件･裁判 | 東洋経済オンライン	https://toyokeizai.net/articles/-/620587?utm_source=rss&utm_medium=http&utm_campaign=link_back	凶悪犯罪	2022-09-28 05:40:00
ビジネス	東洋経済オンライン	転職時は要注意｢放置年金｣110万人の機会損失 本人も気づかぬまま毎月手数料が徴収される | 家計・貯金 | 東洋経済オンライン	https://toyokeizai.net/articles/-/620336?utm_source=rss&utm_medium=http&utm_campaign=link_back	東洋経済オンライン	2022-09-28 05:20:00