了解jQuery源中的空白正则表达式

Question

I was just trying to understand jQuery source of the white space trim REGEX and came across the following:

rtrim = /^[\s\uFEFF\xA0]+|[\s\uFEFF\xA0]+$/g,

Now using a REGEX TOOL , i understood the following:

/^[\s\uFEFF\xA0]+|[\s\uFEFF\xA0]+$/g
1st Alternative: ^[\s\uFEFF\xA0]+
^ assert position at start of the string
[\s\uFEFF\xA0]+ match a single character present in the list below
Quantifier: + Between one and unlimited times, as many times as possible, giving back as needed [greedy]
\s match any white space character [\r\n\t\f ]
\uFEFF matches the character uFEFF literally (case sensitive)
\xA0 matches the character   with position 0xA0 (160 decimal or 240 octal) in the character set
2nd Alternative: [\s\uFEFF\xA0]+$
[\s\uFEFF\xA0]+ match a single character present in the list below
Quantifier: + Between one and unlimited times, as many times as possible, giving back as needed [greedy]
\s match any white space character [\r\n\t\f ]
\uFEFF matches the character uFEFF literally (case sensitive)
\xA0 matches the character   with position 0xA0 (160 decimal or 240 octal) in the character set
$ assert position at end of the string
g modifier: global. All matches (don't return on first match)

The above description makes the REGEX very easy to understand, but still thinking about the implementation practically, a few things don't make sense , IE

uFEFF why would a sting ever have this character and what does it have to do with white spaces ? And also what on earth is xA0 ?

Can anybody explain ? you don't have to give the most detailed answer a short brief one will do.

Answer 1

0xFEFF is known as ZERO WIDTH NO-BREAK SPACE and is possibly not caught on some browsers by using \\s alone. Ditto for 0x00A0 , NO-BREAK SPACE .

See this document for some more detail on what is caught by \\s in ECMA 262 (which is the standard for Javascript.) According to that spec, jQuery is being overly cautious since the characters in question are already included. Likely this is due to browser compatibility.