Question

Reading this discussion, I didn’t understand what this means:

 $1X$2

Simply X?

And about this other code:

 str = str.replace(/(<script.*?>)(.*)(?=<\/script>)/gi, function(x,y,z)
 {return y+z.replace(/a/gi,'Z')})

Here is what I didn’t understand:

• ?=
• how does function(x,y,z) works? i.e. from where it take x, y and z?

I’ll be very grateful if someone could explain in a clear way this code.

Answer 1

The $1 and $2 are referencing the captured sub-expressions (which are delimited by parentheses ()) from the regular expression in the previous argument to .replace().

The ?= is a positive lookahead. http://www.regular-expressions.info/lookaround.html

The function(x, y, z) is an anonymous function expression that does a similar thing to referencing $1 and $2, but it stores them in variables instead.