問題描述

我最近注意到 Web 上的很多 JavaScript 文件都以 ; 開頭，緊跟在評論部分之后.

I have recently noticed that a lot of JavaScript files on the Web start with a ; immediately following the comment section.

例如，這個jQuery插件的代碼以:

/**
 * jQuery.ScrollTo
 * Copyright (c) 2007-2008 Ariel Flesler - aflesler(at)gmail(dot)com | http://flesler.blogspot.com
 * Dual licensed under MIT and GPL.
 * Date: 9/11/2008                                      
 .... skipping several lines for brevity...
 *
 * @desc Scroll on both axes, to different values
 * @example $('div').scrollTo( { top: 300, left:'+=200' }, { axis:'xy', offset:-20 } );
 */
;(function( $ ){

為什么文件需要以 ; 開頭?我在服務器端 JavaScript 文件中也看到了這種約定.

Why does the file need to start with a ;? I see this convention in server-side JavaScript files as well.

這樣做有什么好處和壞處?

What are the advantages and disadvantages of doing this?

推薦答案

我想說，因為腳本經常被連接和縮小/壓縮/發送在一起，所以最后一個人有可能有類似的東西:

I would say since scripts are often concatenated and minified/compressed/sent together there's a chance the last guy had something like:

return {
   'var':'value'
}

在最后一個腳本的末尾沒有 ; 在末尾.如果你有一個 ; 在你的開頭，它是安全的，例如:

at the end of the last script without a ; on the end. If you have a ; at the start on yours, it's safe, example:

return {
   'var':'value'
}
;(function( $ ){ //Safe (still, screw you, last guy!)

<小時>

return {
   'var':'value'
}
(function( $ ){ //Oh crap, closure open, kaboom!

<小時>

return {
   'var':'value'
};
;(function( $ ){ //Extra ;, still safe, no harm

這篇關于為什么 JavaScript 需要以“;"開頭?的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！