regex and javascript

Question

using http://www.regular-expressions.info/javascriptexample.html I tested the following regex

 ^\\{1}([0-9])+ 

this is designed to match a backslash and then a number.

It works there

If I then try this directly in code

var reg = /^\\{1}([0-9])+/;
reg.exec("/123")

I get no matches!

What am I doing wrong?

Answer 1

You need to escape the backslash in your string:

"\\123"

Also, for various implementation bugs, you may want to set reg.lastIndex = 0;. In addition, {1} is completely redundant, you can simplify your regex to /^\\(\d)+/.
One last note: (\d)+ will only capture the last digit, you may want (\d+).

Answer 2

Update:

Regarding the update of your question. Then the regex has to be:

var reg = /^\/(\d+)/;

You have to escape the slash inside the regex with \/.

---

The backslash needs to be escaped in the string too:

reg.exec("\\123")

Otherwise \1 will be treated as special character.

Btw, the regular expression can be simplified:

var reg = /^\\(\d+)/;

Note that I moved the quantifier + inside the capture group, otherwise it will only capture a single digit (namely 3) and not the whole number 123.