regex - JavaScript RegExp objects

Question

I try to write a simple Markdown parser in JavaScript. Therefore I want to check for the [link content][link id] syntax. I use the following code:

data = data.replace( /[(.*?)][ ]*[([0-9]+)]/g, '<a href="$2">$1</a>' );

It works well, but now I want to do this with a RegExp object. So I set up the following bit of code:

var r = new RegExp( '[(.*?)][ ]*[([0-9]+)]', 'g' );
data = data.replace( r, '<a href="$2">$1</a>' );

But it doesn't work. It even says that my regular expression (which works since the first example does a good job) is invalid:

unmatched ) in regular expression

I think it must have to do with some RegExp-object peculiarities I am not aware of. What am I doing wrong and how can the problem be solved?

Answer 1

Because the first argument of the RegExp constructor is a string, not a pattern literal, you have to escape the backslashes, since you want literal backslashes in the pattern:

var r = new RegExp( '\[(.*?)\][ ]*\[([0-9]+)\]', 'g' );