In regular expression: SyntaxError: Unexpected token ]

Question

I used the following expression

str.match(tag+"(\s*=\s*)((['"]*)(.+?)(['"]*)\1)");

where str is the string to be matched with and tag is a variable

For example the above expression should match

m="img"
m='img'

where tag=m;
But at the above mentioned lined I'm getting

SyntaxError: Unexpected token ]

i even tried str.match(tag+"(\s*=\s*)((['\"]*)(.+?)(['\"]*)\1)"); but the result is showing null — user1275375
– user1275375, Commented Apr 9, 2012 at 6:21

dexametason · Accepted Answer · 2012-04-09 06:35:03Z

2

If you remove /1 from the end of the regexp, it works for m="img":

m(\s*=\s*)((['\"]*)(.*)(['\"]*))

"\1" is replaced with the value of the first subpattern within the pattern so if you would like to match m="img";m='img' you should use the following:

(m\s*=\s*)((['\"]*)(.*)(['\"]*)\1)

where m is your tag variable.

EDIT:
you can test your javascript regexps here.

answered Apr 9, 2012 at 6:35

dexametason

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Comments

kirilloid · Accepted Answer · 2012-04-09 06:39:59Z

1

As was stated, quotes should be escaped.
backreference should be escaped too.
once you use backreference, second group with quote is not needed,
it is third parethesis group, which contain quotes, hence you need \3, not \1
and hardly you need to match any amount of quotes like: m = '''img'''

Taking all these points into account, one may get the following solution:

var tag = 'm';
"m='img'".match(tag+"(\s*=\s*)((['\"]?)(.+?)\\3)")
// ["m='img'", "=", "'img'", "'", "img"]

edited Apr 9, 2012 at 6:39

answered Apr 9, 2012 at 6:32

kirilloid

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5 Comments

kirilloid Over a year ago

What is your example, which result in null?

user1275375 Over a year ago

var m="img"; s1 = document.createElement(m); s1.src="cdac.com"; i am retrieving m successfully and for getting the tag name i am using the above expression which is resulting null

kirilloid Over a year ago

Excuse me, but I don't see the code, where you're using this expression.

user1275375 Over a year ago

var m="img"; s1 = document.createElement(m); s1.src="cdac.com";var y=str.match(tag+"(\s*=\s*)((['\"]*)(.+?)\3)");

kirilloid Over a year ago

Maybe, you understood me wrong. I want to see not data, but code, how you are using it. If you mean string with that js code, it is working, i.e. matching m="img".

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