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Functions

There are no functions inside {{ }}. An expression only looks a value up. Arithmetic, comparisons, method calls such as .toLowerCase() or .length, ternaries and functions such as now() or formatDate(…) are not evaluated.

This keeps expressions predictable and safe: a value from a web page or a form can never run as code. Computation happens in nodes, where you can see it, test it and audit it.

What happens if you try

You write What you get
{{ $input.subtotal + $input.tax }} Not a sum. An [EXPR-ERROR: …] marker.
{{ $input.email.toLowerCase() }} Not lower-cased. toLowerCase() is read as a field name, so you get an [EXPR-ERROR: …] marker.
{{ $node["List"].output.items.length }} Not a count. length is read as a field name, so you get an [EXPR-ERROR: …] marker.
{{ now() }}, {{ $now }} Left as literal text. Neither is a Flero root.
{{ $input.name || "Anonymous" }} Not a default. It resolves to null.

Earlier versions of these docs listed arithmetic and a few string methods inside expressions. Flero does not evaluate them.

Use a node instead

You need Use
Build a URL or a message from several values Several blocks in one field: https://{{ $env.API_HOST }}/users/{{ $trigger.payload.userId }}
Upper case, lower case, trim Set node globalTransforms, for example {"lowercase": ["email"], "trim": ["name"]}
A default when a field is missing Set rule with allowOverwrite: false (it only writes a key that isn't there yet), or ?? in a Code node
Join fields Text with several blocks, or a Data Transform concat
Count, sum, average, min, max of a list of numbers Data Transform aggregate
Filter, sort, group, flatten a list Data Transform
Arithmetic Code. Data Transform's calculate only adds fields together.
Format or shift a date Date & Time, or Code
Regex, sentiment, diff Text Processing
Choose between two values An If node with a Set node on each branch, or Code
A later item of a multi-item output No function needed: {{ $node["List Orders"].output._items[2].id }}
Embed an object as JSON text Put it inside other text: Payload: {{ $node["Data"].output.response.body }}. Lists and objects are written as JSON.
Anything else Code

Example: add tax, then use the result.

// Code node "Totals" (JavaScript)
const o = input[0];
return { total: o.subtotal + o.tax };

Downstream: {{ $node["Totals"].output.total }}.

Expressions inside Code

You can put {{ … }} blocks in a Code node's script. Each block is handed to the script as a value, not pasted in as text:

const order = {{ $node["Get Order"].output }};
return { greeting: "Hi {{ $node["Get Order"].output.customerName }}" };

order is a real object, and a quote in the customer's name can't break the script. The same safety applies to Terminal commands and SQL. See Syntax basics → Code, terminal and SQL fields.

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