Backslashes - Regular Expression - Javascript

Question

I wanted to build a JS function concatting a list of arguments to a valid path (since I could not be sure whether a part of the path is given with or without slashes) This is the function: ``` concatPath = function() { var path = ""; for(var i = 0; i < arguments.length; i++) { path += arguments[i].replace("(\|/)$|^(\|/)", "") + "/"; } return path; } ``` The used RegEx matched all beginning and ending slashes and backslashes on http://regexpal.com But the function does not work properly (RegEx does not match). Furthermore, Chrome states SyntaxError: Invalid regular expression: `/(\)$|^(\)/`: Unterminated group when I just use the RegEx ``` (\)$|^(\) ``` However, using the RegEx ``` (\)$|^(\) ``` works fine. Is it too late or did I missed something special? Thanks in advance! Leo

Accepted Answer

You should use a regular expression literal (`/.../`) instead of a string literal (`'...'` or `"..."`) in the call to `replace`. Strings have their own interpretation of backslashes that kicks in before the regular expression constructor gets a crack at it, so you need an extra level of quoting.

Match one backslash, regular expression literal: `/\/`

Match one backslash, regular expression in a string: `'\\'`

But in a regex literal, you also have to put backslashes in front of the forward slashes, since forward slashes are the delimiter for the whole thing:

```
path += arguments[i].replace(/(\|/)$|^(\|/)/, "") + "/";
```

Or, if you're married to the use of strings for some reason, this should also work:

```
path += arguments[i].replace("(\\|/)$|^(\\|/)", "") + "/";
```

As a side note, when your alternatives are single characters, `(x|y)` is overkillish; you can just use a character class (`[xy]`). In which case you get this:

```
path += arguments[i].replace(/[\/]$|^[\/]/, "") + "/";

path += arguments[i].replace("[\\/]$|^[\\/]", "") + "/";
```

Backslashes - Regular Expression - Javascript

Solution

Problem