Getting "error: invalid regular expression"

Question

So I have this code where I'd like to replace all single backslashes with 2 backslashes, for example: \ ---> \\ I tried to do this by the following code:

string = string.replace(new RegExp("\\", "g"), "\\\\");

But apparently this doesn't work because I get the following error:

Uncaught SyntaxError: Invalid regular expression: //: \ at end of pattern

Any idea why?

Answer 1

The \ is a escape character for regular expressions, and also for javascript strings. This means that the javascript string "\\" will produce the following content :\. But that single \ is a escape character for the regex, and when the regex compiler finds it, he thinks: "nice, i have to escape the next character"... but, there is no next character. So the correct regex pattern should be \\. That, when escaped in a javascript script is "\\\\".

So you should use:

string = string.replace(new RegExp("\\\\", "g"), "\\\\"); 

as an alternative, and to avoid the javascript string escape, you can use a literal regex:

string = string.replace(/\\/g, "\\\\");

Answer 2

You escaped the backslash for JavaScript's string literal purposes, but you did not escape it for the regex engine's purposes. Remember, you are dealing with layers of technology here.

So:

string = string.replace(new RegExp("\\\\", "g"), "\\\\");

Or, much better:

string = string.replace(/\\/g, "\\\\");