removal of backslashes in string.

[zeroEvidence]

Prettier Version: 1.5.2 & 1.6.2

Code
No playground, couldn't figure out how to get unique link for my sample.

const decimalNumber = XRegExp('\d\.\d{3}', 'i');

Expected behavior:

const decimalNumber = XRegExp('\d\.\d{3}', 'i');

Actual behavior:

const decimalNumber = XRegExp('d.d{3}', 'i');

[ikatyang]

Hi, those backslashes does nothing there:

I'm not sure if you're attempting to write regex string (should use double backslashes, e.g. '\\d\\.\\d{3}') or want to preserve those unnecessary backslashes?

[ikatyang]

For the playground link, all you have to do is to copy its url :)

[greypants]

@ikatyang this is still a legit issue inside of template literals.

I'm using a markdown tagged template literal to output some documentation, which happens to include the syntax for string interpolation (${}). I need to escape those characters so they're rendered directly instead of interpolated.

Before

markdown`
  const cssString = css\`
    background-color: \$\{color('base')\}
  \`;
`

But prettier is removing the escape backslashes, which causes the content to be interpolated.

Prettier Output:

markdown`
  const cssString = css\`background-color: ${color('base')}\`;
`;

Playground link

[ikatyang]

Can you open a new issue for that? It seems unrelated to this issue, thanks!

EDIT: --> #4377

[ndac-todoroki]

We fell in the similar problem.
When using React Router <Route>, it allows to pass strings which are:

Any valid URL path that path-to-regexp understands.

For example, we pass a string <Route exact path="/path/:id(\d+)" /> (It seems Prettier don't remove backslashes here).

Later in our code, we take out the props.match.path which shows to be the same string as above, and want to perform a switch with other path strings, which are all in an Enum. The deletion happens here.

enum Paths {
  Root = "/",
  Users = "/users",
  UserShow = "/users/:id(\d+)", // <- Prettier deletes the backslash here
}

I wish this could be prevented, because switch matches by the string as-is, not by its regex meanings.

[j-f1]

@ndac-todoroki although the \d in the JSX string is interpreted as the characters \ and d, the \d in the regular string is just interpreted as d, and Prettier removes the now-unnecessary escape. You’ll find that even without running Prettier, the UserShow route won’t work — it’ll actually match /users/ddddddd. Changing it to /users/:id(\\d+) should fix the issue.

[ndac-todoroki]

You were right! Some how I didn't notice it wasn't working :(

[stclairdaniel]

I'm having a similar issue - I have a string like this:
"matchRegexp:(^$)|(^[^!#$%&'\"()*+,/:;<=>?@[\]^{|}~\\]+$)"
and after saving with Prettier, it changes to:
"matchRegexp:(^$)|(^[^!#$%&'\"()*+,/:;<=>?@[]^{|}~\\]+$)"

Note the missing backslash before the close brackets inside the character class. The backslash is being used to escape the close bracket. Without it, the close bracket will be interpreted as the end of the character class. I would just //prettier-ignore it, but I also need to //eslint-disable and I'm not sure how to do both for a single line.

[j-f1]

@stclairdaniel You need two slashes for that to work as you’d expect, and four where you currently have \\.

[stclairdaniel]

Sure enough! I couldn't tell if it was user error or not - thanks for the help.