Odd RegExp behavior

I have been testing regex test string to match the following pattern
(- <any number with/without . decimal point>)
( -[#[.#]] )
here is the code that works the best:

var testStr = '99999+((-25.533) - 5)/99*(-25.533)';
var negValTestStr = new RegExp('\\(\-{1}[0-9]*\.?[0-9]*\\)', 'g');
var test = testStr.match(negValTestStr)
alert(test);


The question is: Why does it only work when the open and close
parenthesis are double escaped: '\\(' and '\\)'
When I use one backslash to escape, it will find -25.533, -5 and -25.533
With two backslashes for escape sequence: (-25.533), (-25.533)

Also, I have to escape the - to get just one -. If I do not escape the -,
-?; which should read - {0, 1} will match --# without escaping -

Thanks for thoughts on this
JK

You need to escape the backslash for it to be interpreted as an escape character itself.
The RegExp constructor is intended for expressions that require the value of a changing variable or variables included within them. Yours could be constructed within //.

If a regular expression is defined by wrapping it in / / characters then you only need to escape characters once.

If a regular expression is defined using RegExp then the expression starts as a text string and so any \ are string escapes that are applied before the string is converted to a regular expression. So any escapes you want to apply to the expression itself need to be double escaped - one for String and one for RegExp.

So in fact you are missing two backslashes in your expression in order for it to work correctly.


RegExp('\\(\\-{1}[0-9]*\\.?[0-9]*\\)', 'g');

or since that is a constant expression it is easier to define it as

/\(\-{1}[0-9]*\.?[0-9]*\)/g;