karatelabs/karate · error · ParserException

missing exponent digits

Error message

missing exponent digits

What it means

A numeric literal contains an exponent marker (`e` or `E`, optionally with sign) but no exponent digits follow. ECMAScript requires at least one digit after the exponent marker, so `1e`, `1.e+`, or `1e-` are rejected at tokenization time.

Solutions

  1. Append the missing exponent digits (`1e` -> `1e10`, `1.e+` -> `1.5e+3`).
  2. Remove the trailing `e`/`e+`/`e-` if the exponent was not intended.
  3. If the value is dynamic, build the number in two parts: `1 * math.pow(10, n)` instead of string-forming `1e${n}`.

Example fix

// before
* def x = 1e
// after
* def x = 1e10
Defensive patterns

Strategy: validation

Validate before calling

// exponent marker must be followed by at least one digit
if (/[eE][+-]?$/.test(expr)) throw new Error('exponent missing digits: ' + expr);

Try / catch

try {
  def x = eval(expr);
} catch (e) {
  if (e.message && e.message.indexOf('missing exponent digits') >= 0) {
    karate.log('incomplete scientific notation: ' + expr);
  }
  throw e;
}

Prevention

When it happens

Trigger: Truncated scientific notation in embedded JS: `1e`, `2.5e+`, `1E-` — caused by incomplete typing, string interpolation cutting off the number, or a template like `1e${x}` where x is empty.

Common situations: Dynamic numeric construction via string concatenation where the exponent variable is empty; copy-paste truncation; accidental insertion of whitespace after `e` inside what should be one number token.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

AI-assisted analysis of karatelabs/karate@a22eb90246 (2026-09-12). Data as JSON: /api/errors/fb735deb82c34080. Report an issue: GitHub.

Appendix: source

Thrown at karate-js/src/main/java/io/karatelabs/parser/JsLexer.java:568

        char p = peek();
        if (p == 'e' || p == 'E') {
            isInteger = false;
            advance();
            if (peek() == '+' || peek() == '-') {
                advance();
            }
            int expDigitsStart = pos;
            while (!isAtEnd() && isDigit(peek())) {
                advance();
            }
            if (!isAtEnd() && peek() == '_') {
                if (pos == expDigitsStart) {
                    throw new ParserException("invalid numeric separator");
                }
                scanDigitsWithSeparators();
            } else if (pos == expDigitsStart) {
                // `1e`, `1.e+` — the exponent marker requires at least one digit
                throw new ParserException("missing exponent digits");
            }
        }

        // Rare path: BigInt suffix — only valid on integer literals
        if (isInteger && !isAtEnd() && peek() == 'n') {
            advance();
            return BIGINT;
        }

        return NUMBER;
    }

    // Slow path: number contained at least one `_` separator. Spec rules:
    //   - `_` must appear between two digits (no leading, trailing, or doubled)
    //   - the first `_` we see has already been validated (preceding char is a digit)
    private void scanDigitsWithSeparators() {
        while (!isAtEnd() && peek() == '_') {
            advance(); // consume `_`

View on GitHub (pinned to a22eb90246)