Function testRegExp

scripts/libs/esprima.js:1084–1125

(pattern, flags)

    }

    function testRegExp(pattern, flags) {
        var tmp = pattern;

        if (flags.indexOf('u') >= 0) {
            // Replace each astral symbol and every Unicode escape sequence
            // that possibly represents an astral symbol or a paired surrogate
            // with a single ASCII symbol to avoid throwing on regular
            // expressions that are only valid in combination with the `/u`
            // flag.
            // Note: replacing with the ASCII symbol `x` might cause false
            // negatives in unlikely scenarios. For example, `[\u{61}-b]` is a
            // perfectly valid pattern that is equivalent to `[a-b]`, but it
            // would be replaced by `[x-b]` which throws an error.
            tmp = tmp
                .replace(/\\u\{([0-9a-fA-F]+)\}/g, function ($0, $1) {
                    if (parseInt($1, 16) <= 0x10FFFF) {
                        return 'x';
                    }
                    throwUnexpectedToken(null, Messages.InvalidRegExp);
                })
                .replace(
                    /\\u([a-fA-F0-9]{4})|[\uD800-\uDBFF][\uDC00-\uDFFF]/g,
                    'x'
                );
        }

        // First, detect invalid regular expressions.
        try {
            RegExp(tmp);
        } catch (e) {
            throwUnexpectedToken(null, Messages.InvalidRegExp);
        }

        // Return a regular expression object for this pattern-flag pair, or
        // `null` in case the current environment doesn't support the flags it
        // uses.
        try {
            return new RegExp(pattern, flags);
        } catch (exception) {
            return null;
        }
    }

    function scanRegExpBody() {
        var ch, str, classMarker, terminated, body;