Using $evaluteExpression for dynamic comparisons

Questions
1

I have a workflow which gets as input equality/inequality expressions which i want to act based upon. I wish to evaluate the value of the expression inside the ‘if’ node and act accordingly. I have seen that theres a utility function $evaluteExpression - but it does not work when i attempt to evalute the whole expression as a string.

For example:
“if {{ $evaluteExpression(1==0) }}” will result in
“if false”
however, the following expression:
“if {{ $evaluteExpression(“1==0” }}” (notice the quotes) will result in
“if 1==0”

my expression is injected from a input parameter, therefore its necessarily a string.

I understand this is probably possible using the code block, but i would very much like to avoid it. Does anyone else have an idea?

  • n8n version: 1.86.0
  • Database: postgresdb
2

This is a classic problem when working with dynamic expressions like strings in n8n, especially if they come as input (e.g. from a table, form, webhook, etc.) and you need to evaluate them as real (boolean) conditions within the flow.

Using Node Code (more flexible and safer), but this is the only reliable way to evaluate a string as a logical expression in JS:

// inputData = { expression: “1 == 0” }

const expression = $json[“expression”]; // ex: “1==0”
let result;

try {
result = eval(expression); // CAUTION: eval can be unsafe with external input
} catch (err) {
result = false;
}

return [{ result }];

You can then use an IF node to check whether result is true or false.