Javascript RegExp string pattern

Question

I need to check JS matches for a dynamically generated string.

ie.

for(i=0; i< arr.length; i++)
{
 pattern_1="/part of "+arr[i]+" string!/i";

 if( string.search(pattern_1) != -1)
  arr_num[i]++;

}

However, this code doesn't work - I presume due to the quotes. How do I do this?

Many thanks.

what are you trying to match? You are correct though, if you neet to dynamically create the regex, you will need to use new RegExp("string");. — Kevin Peno
– Kevin Peno, Commented Jan 8, 2010 at 18:54

Kenan Banks · Accepted Answer · 2010-01-08 18:58:24Z

7

The /pattern/ literal only works as, well, a literal. Not within a string.

If you want to use a string pattern to create a regular expression, you need to create a new RegExp object:

var re = new RegExp(pattern_1)

And in that case, you would omit the enclosing frontslashes (/). These two lines are equivalent:

var re = /abc/g;
var re = new RegExp("abc", "g");

answered Jan 8, 2010 at 18:51

Kenan Banks

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Comments

Rubens Farias · Accepted Answer · 2010-01-08 18:53:09Z

1

Try this:

// note you dont need those "/" and that "i" modifier is sent as second argument
pattern_1= new RegExp("part of "+arr[i]+" string!", "i");

answered Jan 8, 2010 at 18:53

Rubens Farias

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Topher Fangio · Accepted Answer · 2010-01-08 19:02:02Z

1

The problem is that you are passing a string to the search function so it treats it as a string. Try using a RegExp object like so:

myregexp = new RegExp("part of " + arr[i] + " string!", "i")
if (string.search(myregexp) != -1) {
   arr_num[i]++;
}

answered Jan 8, 2010 at 18:52

Topher Fangio

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