Tom Chen tomchentw

What forces layout / reflow

All of the below properties or methods, when requested/called in JavaScript, will trigger the browser to synchronously calculate the style and layout*. This is also called reflow or layout thrashing, and is common performance bottleneck.

Generally, all APIs that synchronously provide layout metrics will trigger forced reflow / layout. Read on for additional cases and details.

Element APIs

Getting box metrics

elem.offsetLeft, elem.offsetTop, elem.offsetWidth, elem.offsetHeight, elem.offsetParent

OS X Screencast to animated GIF

This gist shows how to create a GIF screencast using only free OS X tools: QuickTime, ffmpeg, and gifsicle.

Instructions

To capture the video (filesize: 19MB), using the free "QuickTime Player" application:

從 SocialCalc 到 EtherCalc

先前在《開源應用程式架構》一書中，我介紹了 SocialCalc 這個在瀏覽器中運行的試算表編輯器，以取代伺服器為中心的 WikiCalc 架構。SocialCalc 在瀏覽器中執行所有的運算，只有在載入和儲存試算表時才會使用伺服器。

追求效能是 Socialtext 團隊在 2006 年時設計 SocialCalc 的主要目的。重點在於：在 JavaScript 環境下執行客戶端運算，儘管在當年的速度僅有伺服器端 Perl 運算的十分之一，但仍然勝過 AJAX 來回傳輸資料造成的網路延遲：

******

	FROM alpine:latest

	MAINTAINER Joshua Delsman <j@srv.im>

	EXPOSE 443

	ENV NGINX_VERSION 1.9.3

	RUN apk add --update openssl-dev pcre-dev zlib-dev build-base \
	&& rm -rf /var/cache/apk/* \

	require "rspec/autorun"

	class Enumerator::Lazy
	def reduce(*)
	Lazy.new([nil]) do \|yielder, _\|
	yielder << super
	end
	end

	def join(separator="")

	defaults write org.videolan.vlc NSRecentDocumentsLimit 0
	defaults delete org.videolan.vlc.LSSharedFileList RecentDocuments
	defaults write org.videolan.vlc.LSSharedFileList RecentDocuments -dict-add MaxAmount 0

	defaults write com.apple.QuickTimePlayerX NSRecentDocumentsLimit 0
	defaults delete com.apple.QuickTimePlayerX.LSSharedFileList RecentDocuments
	defaults write com.apple.QuickTimePlayerX.LSSharedFileList RecentDocuments -dict-add MaxAmount 0

	// 原始程式來源: http://practicalcryptography.com/ciphers/enigma-cipher/ 網頁內的 javascript 程式碼

	var c = console;

	var plaintext = 'ABCDEF';
	c.log('>> plaintext2 : '+plaintext);
	var ciphertext = Encrypt(plaintext, 'AAA', 'AAA', '123', 'POMLIUKJNHYTGBVFREDC');
	c.log('>> ciphertext : '+ciphertext);
	var plaintext2 = Encrypt(ciphertext, 'AAA', 'AAA', '123', 'POMLIUKJNHYTGBVFREDC');
	c.log('>> plaintext2 : '+plaintext);