Calculations

Phase 8 evaluates numeric formulas on the server (CalculationEngine) and in the browser (assets/frontend/js/form.js). Posted calculation values are never trusted.

The parser is a recursive-descent evaluator. It does not call eval(), create_function(), or similar.

Field types

Number (number)

Numeric input (type="number") with optional min, max and step (any or a positive number). Empty values are allowed unless the field is required.

Calculation (calculation)

Read-only result of settings.formula. Extra settings: decimals (0–6, default 2), prefix, suffix.

{
  "id": "field_total",
  "type": "calculation",
  "key": "total",
  "label": "Total",
  "required": false,
  "settings": {
    "formula": "{qty} * {price} * 1.19",
    "decimals": 2,
    "prefix": "€ ",
    "suffix": ""
  }
}

Formula syntax

Operators: + - * / and parentheses. Variables:

Form	Meaning
{qty}	Field key qty
{field:qty}	Same, merge-tag style
qty	Bare field key

Missing or non-numeric values count as 0. Hidden fields are empty before the formula runs, so they also count as 0. A field must not use its own key (self-reference is 0).

Functions: min, max, abs, round, floor, ceil. round(x, n) uses n decimal places (0–6).

Invalid expressions, unknown functions, division by zero and oversized results evaluate to 0 on the public form. Saving a form rejects a non-empty invalid formula.

Place quantity/price fields above totals, and totals above fields whose visibility depends on the result.

Runtime

1. SubmitService sanitizes inputs and discards posted calculation values.
2. The engine fills calculation keys in definition order.
3. Visibility (Phase 7) runs; hidden keys are removed.
4. Calculations run again so hidden sources do not affect stored totals.
5. Visible fields are validated. Number min/max apply; calculation fields do not.

{all_fields} and {field:total} in email actions use the server-computed number.

REST catalogue: GET /wp-json/ad-form/v1/calculations (capability edit_ad_form_forms).

PHP:

• Dingfelder\AdForm\Calculations\CalculationEngineInterface
• Dingfelder\AdForm\Calculations\CalculationEngine