JavaScriptテンプレートリテラルのおもしろい例 - Panda Noir
ES2015でテンプレートリテラルが追加されました。テンプレートリテラルには変数を埋め込むことができるのは周知の事実かと思います。しかし、埋めこむことができるのは実は変数、ではなく式です。今回は式を埋め込むことでできるおもしろいコードを紹介しようと思います。 まず三項演算子です。 const arr = [1, 2, 3]; const s = `arr[0] = ${arr.length > 0 ? arr[0] : 'undefined'}`; s === '1'; 式を埋め込むことができるので、当然テンプレートリテラルを埋め込むこともできます。 const hoge = 42; const s = `${`${`${hoge}`}`}`; s === '42'; また、式が有効なものであれば、途中で空白や改行を挟んでもなんの問題もありません。 const hoge = 42; con
Why JavaScript has two zeros: -0 and +0
In pure mathematics, zero means nothing and its sign doesn’t matter. +0 = -0 = 0. Computers can’t represent value well enough and mostly use the IEEE 754 standard. Most languages have two zeros! The IEEE 754 standard for floating point numbers allows for signed zeros, thus it is possible to have both -0 and +0. Correspondingly, 1 / +0 = +∞ while 1 / -0 = -∞ and these are values at opposite ends o
Pitfall: not all objects can be wrapped transparently by proxies
Pitfall: not all objects can be wrapped transparently by proxies A proxy object can be seen as intercepting operations performed on its target object – the proxy wraps the target. The proxy’s handler object is like an observer or listener for the proxy. It specifies which operations should be intercepted by implementing corresponding methods (get for reading a property, etc.). If the handler metho
ECMAScript® 2016 Language Specification
Toggle shortcuts help? Toggle "can call user code" annotationsu Toggle early exit annotationse Navigate to/from multipagem Jump to search box/ Toggle pinning of the current clausep Jump to the nth pin1-9 Jump to the 10th pin0 Jump to the most recent link target` Introduction1 Scope+2 Conformance2.1 Example Normative Optional Clause Heading2.2 Example Legacy Clause Heading2.3 Example Legacy Normati
ES2018: asynchronous iteration
Warning: This blog post is outdated. Instead, read chapter “Asynchronous iteration” in “Exploring JavaScript”. This blog post explains the ECMAScript proposal “Asynchronous Iteration” by Domenic Denicola and Kevin Smith. It has reached stage 4 on 2018-01-25 and is part of ECMAScript 2018. Asynchronous iteration # With ECMAScript 6, JavaScript got built-in support for synchronously iterating over
JavaScriptの配列のパターン
JavaScriptの配列をどう解説するかを考えていて、配列って普段どういう風に使ってるけ?みたいなことを書き出してみました。 Arrayオブジェクト · Issue #49 · asciidwango/js-primer 皆さんは配列をどう使いますか? 追記: 次のページでこの記事をブラッシュアップした話をhttps://jsprimer.net/で公開しています。 配列 · JavaScriptの入門書 #jsprimer 配列の作成 配列の作成には配列リテラル（[]）を使います。 配列リテラルには初期値も指定できます。 var emptyArray = []; // 空の配列を作成 var array = [1, 2, 3]; // 値をもった配列を作成 Arrayオブジェクトをnew演算子でインスタンス化する方法は基本的には使いません。 こちらは配列リテラルとは異なり、初期値ではな
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ES proposal: `global`
Warning: This blog post is outdated. Instead, read section “globalThis” in “Exploring JavaScript”. The ECMAScript proposal “global” by Jordan Harband is currently at stage 3. It provides a new standard way of accessing the global object. Referring to the global object # The following are a few popular ways of referring to the global object: Global variables: Global variable window: is the classic
ES2018: Rest/Spread Properties
Update 2018-01-25: This proposal has reached stage 4 and will be part of ECMAScript 2018. The ECMAScript proposal “Rest/Spread Properties” by Sebastian Markbåge enables: The rest operator (...) in object destructuring. At the moment, this operator only works for Array destructuring and in parameter definitions. The spread operator (...) in object literals. At the moment, this operator only works i
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https://qiita.com/inoinojp/items/e368589c7787823dce4c
dynamic import should be an unary operator · Issue #23 · tc39/proposal-dynamic-import
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JavaScript Authoring Guide
GitHub - kitcambridge/js-history: A repository of historical JavaScript language references.