概念-为什么match（）看似去掉括号？

Question

I did

temp = '(test)';
temp.match(temp);

and got back

0:'test'
1:'test'

Where did the parentheses go?

Update:

Tested in regexpal.com and found similar.

However, switching to {} did not have same concern.

Clarification

temp is "intended" to be a string. Not sure why it would be considered something else.

Answer 1

Parentheses are metacharacters (specifically capturing parentheses ) in regular expressions (note that if you pass a string to the match method it will be implicitly converted to a regular expression). You have to escape them if you want them to be taken literally (since you are dealing with a string, you also have to escape the escape character so that it will still exist when converted to a regex … and by then the regex won't match the original string).

Answer 2

The argument to .match() is treated as a regular expression. Parentheses are meta-characters that mean something in that context. Specifically, they group portions of the matched string. Thus, your regular expression (test) matched the substring "test". The return value gives you the entire match as the first element of the array, and the first group as the second. In this case, because your group covered the whole matched substring, they're the same.

This is the sort of thing that the MDN documentation can quickly clear up:

Parameters

A regular expression object. If a non-RegExp object obj is passed, it is implicitly converted to a RegExp by using new RegExp(obj).

Answer 3

You have to do this:

temp = '\(test\)';
temp.match(temp);

Since () define groups in Regex. look here for more info: http://www.regular-expressions.info/brackets.html

The () are characters used by regex. Just like .*[] etc. That's why it does not return the (). What I've done in the example above is escape them. So the Regex does not see it as a grouping.

Update:

it does work this way:

"(test)".match(/\(test\)/);

When you create a String and have a different Regex Object.