Uncaught SyntaxError: invalid escape sequence in regular expression

[nickwesselman]

While experimenting with a solution that uses javy, I happened to include the camelcase package. When attempting to build, I get the error below.

thread '<unnamed>' panicked at 'called `Result::unwrap()` on an `Err` value: Uncaught SyntaxError: invalid escape sequence in regular expression
    at RegExp (native)
    at <eval> (<input>:10)
    at ./node_modules/camelcase/index.js (script.js:39)
    at __webpack_require__ (script.js:63)
    at <eval> (<input>:2)
    at ./src/index.js (script.js:29)
    at __webpack_require__ (script.js:63)
    at <anonymous> (script.js:115)
    at <anonymous> (script.js:118)
    at webpackUniversalModuleDefinition (script.js:15)
    at <eval> (script.js:120)
', crates/core/src/lib.rs:35:61
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
Error: the `wizer.initialize` function trapped

Caused by:
    wasm trap: wasm `unreachable` instruction executed
    wasm backtrace:
        0: 0xcb9d9 - <unknown>!__rust_start_panic
    note: using the `WASMTIME_BACKTRACE_DETAILS=1` environment variable to may show more debugging information

Error: Couldn't create wasm from input

Reproduction here, I was able to isolate the issue to the following lines in camelcase:

const IDENTIFIER = /([\p{Alpha}\p{N}_]|$)/u;
const SEPARATORS = /[_.\- ]+/;
const LEADING_SEPARATORS = new RegExp('^' + SEPARATORS.source);

// THIS LINE APPEARS TO BE THE ISSUE
const SEPARATORS_AND_IDENTIFIER = new RegExp(SEPARATORS.source + IDENTIFIER.source, 'gu');

Not sure what the exact issue is, or how common it might be in other code.

[saulecabrera]

Good catch. I spent some time investigating this and I was able to the get to the bottom of the issue: passing the unicode flag to a regular expression puts the regular expression engine in "strict mode", in plain words this means that some escape sequences, such as \-, \: will be considered erroneous (ref); in that sense the error can be considered expected, what's unexpected here is the behaviour across engines, in V8 for example, using the RegExp constructor and passing the u flag, doesn't cause an error, but when constructing the regular expression through a literal with an invalid escape sequence, the error appears:

var r = new RegExp("\-", 'u');
console.log(r) //  /-/u => the escape was removed

// vs 

/\:/u // Results in Invalid regular expression: /\:/: Invalid escape