November 2020
Intermediate to advanced
740 pages
9h 12m
Japanese
Content preview from ハンズオンJavaScriptBecome an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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7章コレクションを学ぶ
「2章 データを学ぶ」でデータをまとめる手段のひとつとして配列を紹介しました。配列リテラルが実際に生成するのはArrayオブジェクトですが、JavaScriptにはそのほかにもデータをまとめて扱うためのオブジェクトがあり、そのようなオブジェクトを総称してコレクションと呼びます。JavaScriptのコレクションは大きく分けて2種類です。ひとつがインデックス付きコレクション（indexed collection）で、順序づけて保持している要素を[]と数値を使用して指定できます。ここにはすでに紹介した配列と、本章で初めて紹介する型付き配列が含まれます。もうひとつがキー付きコレクション（keyed collection）で、任意のオブジェクトをキーとして、要素を関連づけて保持し、そのキーを使用して要素を指定できます。ここに含まれるオブジェクトはMap、Set、WeakMap、WeakSetの4つです。「4章 オブジェクトを学ぶ」で紹介したObjectも複数の要素を保持して文字列型またはシンボル型のキーでそれらを取り出せますが、Objectはそれ以外にもさまざまな役割があるため、一般にコレクションには含まれません。
本章ではそれぞれのコレクションオブジェクトを順に紹介し、さらにそれらのコレクションオブジェクトの走査を統一的に扱う手段であるイテレータについて説明します。
7.1 Array
Arrayは最も基本的なコレクションである配列を表すオブジェクトです。配列にはコレクションとして唯一リテラル表記が用意されていて、new演算子を使用せずにオブジェクトを生成できます。インデックスを使用した要素へのアクセスなどの基本的な使用方法についてはすでに「2章 データを学ぶ」で説明しているので、ここではメソッドを使用したより進んだ配列の操作について説明します。 ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.