The Code Node

Two modes

The Code node runs JavaScript (or Python). In Run Once for All Items mode you read every item with $input.all() and must return an array of { json: {...} }. In Run Once for Each Item mode you read $input.item and return one { json: {...} }. Choose all-items mode for dedupe, sorting and aggregation, and each-item mode for simple per-record changes.

Normalise and dedupe (all items)

I ran this logic in Node.js with sample items. Two input rows had the same email, so one is dropped, and the non-numeric amount "abc" becomes NaN, which JSON prints as null.

const seen = new Set();
const out = [];
for (const item of $input.all()) {
  const email = item.json.email.trim().toLowerCase();
  if (seen.has(email)) continue;          // drop duplicates
  seen.add(email);
  out.push({ json: {
    name: item.json.name.trim(),
    email,
    amount: Number(item.json.amount),
  }});
}
return out;

Output:

[{"json":{"name":"Asha","email":"asha@example.com","amount":1200}},
 {"json":{"name":"Ravi","email":"ravi@example.com","amount":null}}]

Validate before you continue

Filtering out rows whose amount is not a finite number keeps bad data out of the next system. On the same sample, 1 row is valid and 1 is rejected.

const valid = out.filter(i => Number.isFinite(i.json.amount));
const invalid = out.length - valid.length;
return valid;   // log or route the invalid ones elsewhere

Output:

1 valid, 1 invalid

Return the right shape

Returning plain objects instead of { json: ... } items is the most common Code node error. When something looks wrong, check the node's output tab and read the error message; it names the expected shape.

Quick check: What must a Code node in "all items" mode return?

• A plain string
• Nothing
• An array of objects with a json property
• A number