karatelabs/karate · error · ParserException

invalid binary literal

Error message

invalid binary literal

What it means

Karate's embedded JS lexer throws this when it sees a `0b` prefix but no binary digit (0 or 1) follows. The lexer requires at least one valid binary digit after the `0b`/`0B` marker, matching the ECMAScript numeric literal grammar. It is a ParserException raised during tokenization, before parsing.

Solutions

1. Add at least one binary digit after the `0b` prefix (e.g. `0b1010` instead of `0b`).
2. Remove the `0b` prefix if a decimal value was intended (e.g. `0b` -> `0`).
3. Check the character immediately after `0b` — only `0` and `1` are valid; `2`-`9` or `_` start the literal incorrectly.
4. Escape or move the text out of JS context if `0b` is not meant to be a literal (e.g. inside a string).

Example fix

// before
* def x = 0b
// after
* def x = 0b1010

// validate before passing to karate eval
function isValidJsNumberLiteral(s) {
  return /^0[bB][01]+n?$/.test(s.trim());
}
if (!isValidJsNumberLiteral(expr)) throw new Error('bad binary literal: ' + expr);

try {
  def x = eval(expr);
} catch (e) {
  if (e.message && e.message.indexOf('invalid binary literal') >= 0) {
    karate.log('malformed binary literal, fix 0b usage: ' + expr);
  }
  throw e;
}

When it happens

Trigger: Writing JS in a Karate script with a malformed binary literal such as `0b`, `0b2`, `0b_1`, or `0B` — the `0b` is immediately followed by a non-binary character or end of token.

Common situations: Typo in a bitwise operation or numeric constant inside embedded JS expressions (`karate.js`, `eval` blocks, `* assert` steps); hand-editing constants and dropping a digit; copy-pasted code where digits after `0b` were lost.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• invalid numeric separator
• invalid octal literal
• missing exponent digits
• invalid escape sequence in template literal: \
• invalid escape sequence in template literal: \0

AI-assisted analysis of karatelabs/karate@a22eb90246 (2026-09-12). Data as JSON: /api/errors/bdabeb607a09cdb1. Report an issue: GitHub.

Appendix: source

Thrown at karate-js/src/main/java/io/karatelabs/parser/JsLexer.java:480

            }
            // Rare path: BigInt suffix — `0xff_ffn` is valid
            if (!isAtEnd() && peek() == 'n') {
                advance();
                return BIGINT;
            }
            return NUMBER;
        }

        // Binary number (0b / 0B)
        if (c == '0' && (peek(1) == 'b' || peek(1) == 'B')) {
            advance(); // 0
            advance(); // b
            int binStart = pos;
            while (!isAtEnd() && (peek() == '0' || peek() == '1')) {
                advance();
            }
            if (pos == binStart) {
                throw new ParserException("invalid binary literal");
            }
            if (!isAtEnd() && peek() == '_') {
                scanBinaryDigitsWithSeparators();
            }
            if (!isAtEnd() && peek() == 'n') {
                advance();
                return BIGINT;
            }
            return NUMBER;
        }

        // Octal number (0o / 0O)
        if (c == '0' && (peek(1) == 'o' || peek(1) == 'O')) {
            advance(); // 0
            advance(); // o
            int octStart = pos;
            while (!isAtEnd() && peek() >= '0' && peek() <= '7') {
                advance();

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