Invalid regular expression flag

[yllhwa]

reproduction code:

const espree = require("espree");
var code = `let pattern = /(\/x\/[\w-_]+\/)/;`;
var ast = espree.parse(code, { ecmaVersion: 6 });
console.log(ast);

the regular expression looks fine(since I can run the code below)

let url = "/pre/x/test/";
url = url.replace(/(\/x\/[\w-_]+\/)/, "$1append/")
console.log(url)

but an error occurred:

espree\dist\espree.cjs:679
            throw err;
            ^

SyntaxError: Invalid regular expression flag
    at Espree.raise (espree\dist\espree.cjs:674:25)
    at pp$1.validateRegExpFlags (acorn\dist\acorn.js:3945:14)
    at pp.readRegexp (acorn\dist\acorn.js:5540:10)
    at pp.readToken_slash (acorn\dist\acorn.js:5315:53)
    at pp.getTokenFromCode (acorn\dist\acorn.js:5478:19)
    at pp.readToken (acorn\dist\acorn.js:5195:17)
    at pp.nextToken (acorn\dist\acorn.js:5186:17)
    at pp.next (acorn\dist\acorn.js:5147:10)
    at pp$9.eat (acorn\dist\acorn.js:702:12)
    at pp$8.parseVar (acorn\dist\acorn.js:1320:16) {
  index: 15,
  lineNumber: 1,
  column: 16
}

Node.js v20.10.0

version: 9.6.1

[fasttime]

Note that backslash characters in template literals create escape sequences, so the code in your example is not what it looks like:

var code = `let pattern = /(\/x\/[\w-_]+\/)/;`;
console.log(code);

// prints "let pattern = /(/x/[w-_]+/)/";

To get the text as it appears inside backticks, you could use String.raw:

var code = String.raw`let pattern = /(\/x\/[\w-_]+\/)/;`;

Or insert a double backslash (\\) where there should be one:

var code = `let pattern = /(\\/x\\/[\\w-_]+\\/)/;`;

[yllhwa]

Thanks a lot. I just made such a silly mistake. Esprima cannot parse this, so I want to try espree. And it works!