Expected Behavior

Obfuscating an untagged template literal such as `Today: ${when}` should convert each substituted expression to a string using ToString (calling toString before valueOf, or passing the "string" hint to Symbol.toPrimitive), matching the runtime behavior of the original code (e.g. printing Today: Tue Nov 14 2023). Lowering template literals to ''.concat(...) preserves ES5 compatibility while calling ToString on each argument.

Current Behavior

JavaScriptObfuscator.obfuscate rewrites untagged template literals into '...' + expr binary expressions across all presets. For objects that define both valueOf and toString (such as Moment.js/Day.js instances or Decimal wrappers) or Symbol.toPrimitive, + invokes ToPrimitive with the "default" hint instead of ToString ("string" hint), so the obfuscated code calls valueOf instead of toString and prints Today: 1700000000000.

Steps to Reproduce

1. Define an object with both valueOf and toString (or Symbol.toPrimitive) and interpolate it inside a template literal.
2. Obfuscate the code with JavaScriptObfuscator.obfuscate(code).
3. Execute both the original and obfuscated code and compare their output.

JavaScript Obfuscator Edition

• JavaScript Obfuscator Open Source

Your Environment

• Obfuscator version used: 5.10.0
• Node version used: v24.14.1

Stack trace

N/A (wrong runtime output, no exception thrown)

Minimal working example that will help to reproduce issue

const JavaScriptObfuscator = require('javascript-obfuscator');

const code = `
var when = { valueOf() { return 1700000000000; }, toString() { return "Tue Nov 14 2023"; } };
console.log(\`Today: \${when}\`);
`;

eval(code);
// Output: Today: Tue Nov 14 2023

eval(JavaScriptObfuscator.obfuscate(code).getObfuscatedCode());
// Output: Today: 1700000000000

Credit: https://ucsbplse.github.io/