Expressions

Text, visibility, filters, sorting and conditions use JavaScript expressions. In text they go inside {{ }}:

Total: {{ sum(rows, r => r.total) }}

Expressions are evaluated by a built-in interpreter. They never run through eval or new Function.

Supported: literals, template literals, arrays and objects, . / [] / ?., calls, arrow functions with expression bodies, ! - + typeof, arithmetic, comparison, && || ?? and ? :.

Not supported: assignment, statements, new, this, function, class, loops, regular expressions.

A text that is a single {{ expression }} keeps the value’s type, so numbers and dates can be formatted and exported to Excel as typed cells. Use \{{ for a literal {{.

Variables

Name	Meaning
row	current row (detail, group and child bands)
rowNumber	1-based row number within the region
rows	all rows of the region, after filter and sort
group	{ key, rows, count, index, level } of the innermost group
groups	all active groups, outermost first
parent	the parent row inside a child region
params	parameter values
page	{ number, count, regions }, see Running totals
report	{ name, description }
<dataSource>	every data source by name, e.g. orders

Functions

Group	Functions
Aggregates	sum avg min max count first last distinct. Each takes an array and an optional field name or r => … selector.
Numbers	round floor ceil abs, and a safe Math
Text	upper lower trim len left right
Values	string number isNull isEmpty coalesce iif
Dates	now today date year month day addDays addMonths dateDiff
Formatting	format formatNumber formatCurrency formatPercent formatDate
Words	toWords(n) and toCurrencyWords(amount, currencyName, centsName) (English)

Strings, numbers, arrays and dates expose the usual read-only methods (map, filter, reduce, some, join, toUpperCase, padStart, toFixed, getFullYear, …). sort and reverse return copies.

{{ iif(row.stock < 10, 'Low', 'OK') }}
{{ upper(row.name) }} ({{ row.qty }} × {{ formatCurrency(row.price, 'USD') }})
{{ formatDate(today(), 'd MMMM yyyy') }}
{{ distinct(orders, 'customer').length }} customers
{{ toCurrencyWords(1250.5, 'Dollars', 'Cents') }}

Your own functions

Add functions with the functions option. Only these functions (and the built-ins) can be called from a template:

import { generateReport } from '@ariana-reports/core';

generateReport(template, data, { functions: { vat: (n: number) => n * 0.09 } }); // {{ vat(row.total) }}

The viewer components take the same functions prop.

Safety

Expressions can only read own properties of your data. window, globals, prototypes and constructor are unreachable, functions found in the data cannot be called, and every evaluation has limits on steps (maxSteps), call depth, string length and array size. An expression that loops forever or builds a huge array stops with an error instead of freezing the page.

Errors

An expression that fails at run time shows #ERROR in its text box and is listed in document.issues and in the viewer’s Issues panel. The rest of the report still renders. Syntax errors are caught earlier, by validation and in the designer as you type.