n8n-docs/docs/code-examples/methods-variables-examples/evaluate-expression.md

$evaluateExpression(expression: string, itemIndex?: number)

Evaluates a given string as expression.

If you don't provide itemIndex, n8n uses:

• The data from item 0 in the Function node.
• The data from the current item in the Function Item node.

Example:

items[0].json.variable1 = $evaluateExpression('{{1+2}}');
items[0].json.variable2 = $evaluateExpression($node["Set"].json["myExpression"], 1);

return items;