问题
Bookmarklets I've made seem to always work well even though I don't escape them, so why do bookmarklet builders like John Gruber's escape special characters like space to %20?
回答1:
If you copy/paste code into a bookmark using the browsers bookmark properties editor, you don't need to encode anything except newlines and percent signs. But, in fact, Firefox (and maybe other browsers) will encode spaces for you. If you check the properties again after saving, you'll see them encoded. You need to encode newlines because a bookmark can be only 1 line. You need to encode percent signs because the browser expects percent sights to always represent the first character in an encoded set. If you put the bookmarklet on a website in the HREF property of an A tag, the same rules apply, but you must also either HTML encode or URL encode any double quotes.
A lot of bookmarklet makers will just use encodeURIComponent, which encodes more than what is strictly necessary, but it might be considered more "correct".
来源：https://stackoverflow.com/questions/20066180/when-is-it-necessary-to-escape-a-javascript-bookmarklet