Inject bindVar into comment part of an AQL query

[matcho]

Hello, is it possible to achieve something like the following using arangojs : inject a JS variable inside a comment of an AQL query?

For ex:

const myVar = "I'd like to see this in the query string, in a comment";
const query = AQL`
  // FYI: ${myVar} :)
  for doc in coll
    (…)
`;
db.query(query);

Running the code above leads to: Uncaught ArangoError: bind parameter 'value0' was not declared in the query

Tried this too:

const myVar = "// I'd like to see this in the query string, in a comment";
const query = AQL`
  ${myVar}
  for doc in coll
    (…)
`;
db.query(query);

→ Uncaught ArangoError: syntax error, unexpected bind parameter near '@value0

Thanks,
Best regards

[bluepal-yaswanth-peravali]

Hi @matcho, thanks for the examples.

This behavior is expected. The aql tag does not actually parse AQL—it simply converts each ${…} into a bind parameter like @value0.

In AQL, any line starting with // is treated as a comment, so everything on that line (including something like @value0) is ignored by the query parser. However, the client still sends the corresponding bind value, which leads to a mismatch between declared and used bind parameters.

In your second example, the interpolation is replaced with @value0, not the literal string content, which is why you encounter a syntax error.

A practical approach is to keep the query string strictly limited to executable AQL and avoid placing dynamic values inside commented lines. If you need to include context or debug information, logging it alongside the query is usually clearer and avoids this issue.

This edge case isn’t currently documented in the driver. We’ll add a short note to the aql documentation to help prevent similar confusion in the future.