投稿時間:2022-07-16 23:11:10 RSSフィード2022-07-16 23:00 分まとめ(14件)

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Linux	Ubuntuタグが付けられた新着投稿 - Qiita	ubuntu でMozcをいれる方法	https://qiita.com/kazu77/items/0bcd4d7cf2d2a95156cb	inputsourcessources	2022-07-16 22:59:26
golang	Goタグが付けられた新着投稿 - Qiita	【#31 エンジニア転職学習】Go WebApplications　DB操作	https://qiita.com/Chika110/items/f00c6c7491aebd8e57c8	chika	2022-07-16 22:24:54
海外TECH	DEV Community	How does Optional Chaining work in Javascript?	https://dev.to/smpnjn/how-does-optional-chaining-work-in-javascript-55ke	How does Optional Chaining work in Javascript Optional chaining is a feature in Javascript which lets us access child properties of an object even if the parent object doesn t exist It s used when properties are optional on an object so that instead of returning an error we still get a result from Javascript Let s look at how it works Introduction to Optionality in JavascriptAnyone who has used Javascript for any length of time may have run into a pretty common issue where accessing a child property which is optional requires a lot of additional logic to test it exists before we do anything As an example imagine an article building piece of software where the object article may have a child property called relatedArticle and within that we may have some basic information on a related article Let s imagine we access a related article s URL by article relatedArticle url however not every article will have a related article Traditionally in Javascript assuming article is defined we may have written something like this let article let url if article relatedArticle undefined url article relatedArticle url Or we may be tempted to try something like this instead let article let url article relatedArticle article relatedArticle undefined This ultimately avoids the following error should relatedArticle be undefined Cannot read properties of undefined reading url If we have multiple child levels though we can end up writing quite a long string of undefined statements This can get quite tedious and out of control for very big objects For example below we try to access article relatedArticle url rootDomain when we aren t really sure if these objects will be defined let article let rootDomain if article relatedArticle undefined amp amp article relatedArticle url undefined rootDomain article relatedArticle url rootDomain Optionality solves this problem of excessive undefined checks If something is given an optional tag then if it exists the value will be returned otherwise it will not throw an error In the above example we don t even really need an if statement anymore let article let rootDomain article relatedArticle url rootDomain By adding should relatedArticle or url be undefined or null it will simply pass onto the next property without throwing an error We can even improve this by setting a default value using nullish coalescing Below if the rootDomain property is found to be undefined it will instead return let article let rootDomain article relatedArticle url rootDomain How to use Optional Chaining in JavascriptIn most examples you can use optional chaining as described above to avoid errors on truly optional properties within an object let article let rootDomain article relatedArticle url rootDomain One caveat to this is that you cannot add a question mark to the end of an object The following will therefore throw an error let article let rootDomain article relatedArticle url rootDomain Will throw an error like Unexpected token Although this is the most common way to use optional chaining there are other ways to implement it in your code Let s explore those too to see the full extent of how to use optional chaining in your code and projects When to not use optional chainingNote you should NOT use optional chaining to simply avoid errors If you overuse optional chaining you will silence errors and make it much more difficult to debug your code later Instead only use optional chaining for REAL optional properties Optional Chaining with FunctionsYou can use optional chaining with functions which you expect may return objects It works exactly the same as before only we add after the function myFunction arguments x let myFunction x y z gt if z undefined return x x y y z z let arguments let getX myFunction arguments x console log getX Returns It s good to know at this stage that by default if a function has no return it returns undefined so this can be quite useful in situations where you are not sure a function will return anything at all Optional Chaining with ArraysOptional chaining can also be used with arrays For example if you aren t sure if a property will be defined but it contains an array Below a user can have an array of valid addresses and we want to get the first line of their address from their first address Since it may not always exist we can use optional chaining here to try and recover it let myUser name John Doe age let getAddress myUser addresses firstIn this case addresses is not defined on myUser so getAddress will simply return undefined If we want to check a property which should be array the notation is obj prop index while if we want to check an array index which may not exist but has child elements within the notation is obj index prop Optional Chaining with Optional FunctionsSometimes the return of an object property may be a function In these cases we may want to run this function but since it isn t always defined we only want it to fire if it s there In this case we can use the notation to run the function should it exist Consider the following example let myObject id adder x gt return x id myObject forEach item gt let runFunction item adder console log runFunction Above we have an object which contains an array where each object contains an id id and may also contain the function adder In this example we want to run this adder function if it exists or default the value to if the function is undefined so we run the function let runFunction item adder Here if adder is defined it runs so we get x or for the first element of the array and simply for the second since adder does not exist ConclusionOptional Chaining is incredibly useful and widely supported excluding Internet Explorer It can be used with pretty much any combination of property array or function depending on return types For example obj propertyobj property obj index propertyobj args func args propertyOptional chaining is therefore a great way to simplify your code and gives syntax and meaning to real optional properties within your objects	2022-07-16 13:10:22
Apple	AppleInsider - Frontpage News	Daily deals July 16: $192 Anycubic resin 3D printer, $170 AirPods Pro, $130 Cuisinart AirFryer, more	https://appleinsider.com/articles/22/07/16/daily-deals-july-16-192-anycubic-resin-3d-printer-170-airpods-pro-130-cuisinart-airfryer-more?utm_medium=rss	Daily deals July Anycubic resin D printer AirPods Pro Cuisinart AirFryer moreSaturday s best deals include off a inch Apple Leather Sleeve a Sapphire Pulse Radeon RX XT graphics card and much more Best deals for July Every day AppleInsider scours online retailers to find discounts on products including Apple hardware mobile devices hardware upgrades smart TVs and accessories The best offers we find are put together in our daily deals post Read more	2022-07-16 13:21:06
ニュース	@日本経済新聞 電子版	円相場、理論値より割安 　日経均衡為替レートは109円台 https://t.co/Q48Bi3I4Mw	https://twitter.com/nikkei/statuses/1548296307709595648	為替レート	2022-07-16 13:19:40
海外ニュース	Japan Times latest articles	G20 finance talks end without joint statement amid rift over Ukraine	https://www.japantimes.co.jp/news/2022/07/16/business/economy-business/g20-finance-ministers-communique-ukraine/	G finance talks end without joint statement amid rift over UkraineFinance chiefs from the Group of major economies fell short of issuing a joint statement due to their rift over Russia s war in Ukraine	2022-07-16 22:06:49
ニュース	BBC News - Home	UK heatwave: Stay safe to avoid excess deaths in hot weather - health boss	https://www.bbc.co.uk/news/uk-62189515?at_medium=RSS&at_campaign=KARANGA	agency	2022-07-16 13:13:55
ニュース	BBC News - Home	Europe heatwave: Deadly wildfires spread in Mediterranean	https://www.bbc.co.uk/news/world-europe-62189272?at_medium=RSS&at_campaign=KARANGA	costa	2022-07-16 13:35:08
ニュース	BBC News - Home	Tory leadership rivals trade blows over tax and spending	https://www.bbc.co.uk/news/uk-politics-62186878?at_medium=RSS&at_campaign=KARANGA	blows	2022-07-16 13:53:06
ニュース	BBC News - Home	Robert Lewandowski: Barcelona reach agreement with Bayern Munich to sign Poland striker	https://www.bbc.co.uk/sport/football/62191722?at_medium=RSS&at_campaign=KARANGA	lewandowski	2022-07-16 13:48:17
北海道	北海道新聞	アラブ原油増産に期待　米大統領「今後数カ月」	https://www.hokkaido-np.co.jp/article/706709/	米大統領	2022-07-16 22:20:31
北海道	北海道新聞	道内太平洋側、１７日夜にかけて大雨　ＪＲ８３本運休	https://www.hokkaido-np.co.jp/article/706707/	太平洋側	2022-07-16 22:10:08
北海道	北海道新聞	地域と連携し考古学研究、東大院　鳥取・米子で記念シンポジウム	https://www.hokkaido-np.co.jp/article/706710/	鳥取	2022-07-16 22:21:00
北海道	北海道新聞	容疑者負債６０万、困窮し犯行か　安倍元首相襲撃、「７月に決意」	https://www.hokkaido-np.co.jp/article/706698/	安倍元首相	2022-07-16 22:06:06