Expression reference · Docs

Expressions are a safe subset of JavaScript. This page lists everything they can use. The editor’s autocomplete is built from the same definitions, so this list is always complete.

The same list is in the Reference zone of the Expression Studio, where a click inserts a function at the cursor.

Syntax

// Arithmetic       + - * / % **
// Comparison       == != === !== < > <= >=
// Logic            && || ! ?? and  cond ? a : b
// Access           a.b  a[b]  a?.b
// Literals         'text'  `Hi ${user.name}`  [1, ...list]  { a: 1, ...obj }
// Lambdas          items.filter(x => x.price > 10)   (as call arguments only)

Scope

Name	Holds	Available
`vars`	page and site variables	everywhere
`queries`	`{ data, loading, error, updatedAt }` per query	pages
`item`, `index`, `parent`	the current row, its position, the enclosing row	collection lists, template pages
`page`	`path`, `params`, `query`	pages
`site`	`name`, `locale`	everywhere
`user`	the visitor, `{ isLoggedIn: false }` when signed out	everywhere
`steps`, `input`, `event`, `error`	step results, workflow input, the triggering event, a caught error	workflows
`row`	the row being read or written	row rules
`fn`	built-in functions below and your formulas	everywhere

Functions

Call built-ins as fn.name(…). Arguments marked ? are optional. Key arguments accept a field path ('author.name') or a lambda.

Formatting

Function	Returns	Description
`fn.formatNumber(value, decimals?, locale?)`	`string`	Locale-formatted number with grouping. decimals is a fixed number of decimals or Intl.NumberFormat options ({ notation: "compact" }, { style: "percent" }). Empty string for null/undefined. `fn.formatNumber(1234.5, 2, 'en-US') // '1,234.50'`
`fn.formatCurrency(value, currency?, locale?, decimals?)`	`string`	Locale-formatted money amount (currency: ISO 4217 code, default USD). `fn.formatCurrency(item.price, 'EUR', 'de-DE') // '12,50 €'`
`fn.formatDate(date, format?, locale?, timeZone?)`	`string`	Locale-formatted date. Formats: short, medium (default), long, full, datetime, time, iso, isoDateTime, or Intl.DateTimeFormat options. Time zone defaults to UTC. `fn.formatDate(item.publishedAt, 'long', 'en-GB') // '1 March 2026'`

Dates

Function	Returns	Description
`fn.now()`	`date`	Current time as an ISO string. `fn.now()`
`fn.dateAdd(date, amount, unit)`	`date`	Adds an amount of a unit (year, quarter, month, week, day, hour, minute, second). UTC; month math clamps to the last day. `fn.dateAdd(fn.now(), 7, 'day')`
`fn.dateDiff(from, to, unit?)`	`number`	Whole units from from to to (default day; negative when to is earlier). `fn.dateDiff(item.publishedAt, fn.now(), 'day')`
`fn.startOf(date, unit)`	`date`	Start of the unit containing the date (UTC; weeks start on Monday). `fn.startOf(fn.now(), 'month')`

Text

Function	Returns	Description
`fn.truncate(text, length, suffix?)`	`string`	Cuts to length characters (suffix included, default …) when longer. `fn.truncate(item.excerpt, 120)`
`fn.slugify(text)`	`string`	Kebab-case ASCII slug (Café Ñandú → cafe-nandu).

Arrays

Function	Returns	Description
`fn.length(value)`	`number`	Items in an array, characters in a string, keys in an object; 0 otherwise.
`fn.sum(items, key?)`	`number`	Sum of the numeric values (non-numbers skipped). `fn.sum(queries.cart.data, 'price')`
`fn.avg(items, key?)`	`number`	Average of the numeric values; null when there are none.
`fn.uniq(items, key?)`	`array`	Items with duplicates removed (by deep value, or by key).
`fn.groupBy(items, key)`	`object`	Object of arrays keyed by the key value. `fn.groupBy(queries.products.data, 'category')`
`fn.sortBy(items, key?, direction?)`	`array`	Sorted copy (asc default or desc): numbers numerically, strings by code point, null last. `fn.sortBy(items, 'price', 'desc')`
`fn.range(start, end?, step?)`	`array`	Numbers from start (inclusive) to end (exclusive); fn.range(3) → [0, 1, 2].

Math

Function	Returns	Description
`fn.min(...values)`	`any`	Smallest value: fn.min(1, 2), fn.min(items, "price").
`fn.max(...values)`	`any`	Largest value: fn.max(1, 2), fn.max(items, "price").
`fn.round(value, decimals?)`	`number`	Rounds half away from zero to decimals places (default 0).

Objects

Function	Returns	Description
`fn.keys(object)`	`array`	Own keys.
`fn.values(object)`	`array`	Own values.
`fn.entries(object)`	`array`	[key, value] pairs.

Logic

Function	Returns	Description
`fn.default(value, fallback)`	`any`	The fallback when the value is null, undefined or "". `fn.default(item.subtitle, 'Untitled')`
`fn.toNumber(value, fallback?)`	`number`	Number from a number or numeric string; the fallback (default null) otherwise.

JSON

Function	Returns	Description
`fn.jsonStringify(value, indent?)`	`string`	JSON text (forbidden keys dropped; oversized values are errors).
`fn.jsonParse(text, fallback?)`	`any`	Parses JSON; the fallback (default null) when invalid. __proto__/constructor keys are dropped.

Methods

Values also have the familiar JavaScript methods. Methods never change the original: sort and reverse return copies.

Text methods

Method	Returns	Description
`.length`	`number`	Number of UTF-16 code units.
`.toUpperCase()`	`string`	Upper-case copy.
`.toLowerCase()`	`string`	Lower-case copy.
`.trim()`	`string`	Removes leading and trailing whitespace.
`.trimStart()`	`string`	Removes leading whitespace.
`.trimEnd()`	`string`	Removes trailing whitespace.
`.startsWith(search, position?)`	`boolean`	True when the string starts with search.
`.endsWith(search, length?)`	`boolean`	True when the string ends with search.
`.includes(search)`	`boolean`	True when search occurs in the string.
`.indexOf(search, from?)`	`number`	First index of search, or -1.
`.lastIndexOf(search)`	`number`	Last index of search, or -1.
`.slice(start?, end?)`	`string`	Part of the string (negative indexes count from the end).
`.substring(start, end?)`	`string`	Part of the string between two indexes.
`.split(separator, limit?)`	`array`	Splits on a literal separator.
`.replace(search, replacement)`	`string`	Replaces the first literal occurrence.
`.replaceAll(search, replacement)`	`string`	Replaces every literal occurrence.
`.padStart(length, fill?)`	`string`	Pads the start to length.
`.padEnd(length, fill?)`	`string`	Pads the end to length.
`.repeat(count)`	`string`	The string repeated count times.
`.charAt(index)`	`string`	Character at an index.
`.at(index)`	`string`	Character at an index (negative counts from the end).
`.concat(...parts)`	`string`	Appends the parts.
`.localeCompare(other, locale?)`	`number`	Locale-aware comparison (-1, 0, 1).
`.toString()`	`string`	The string itself.

Array methods

Method	Returns	Description
`.length`	`number`	Number of items.
`.map(callback)`	`array`	New array with the callback result for each item: (item, index) => ….
`.filter(callback)`	`array`	Items for which the callback is truthy.
`.find(callback)`	`any`	First item for which the callback is truthy.
`.findIndex(callback)`	`number`	Index of the first match, or -1.
`.findLast(callback)`	`any`	Last item for which the callback is truthy.
`.findLastIndex(callback)`	`number`	Index of the last match, or -1.
`.some(callback)`	`boolean`	True when the callback is truthy for any item.
`.every(callback)`	`boolean`	True when the callback is truthy for every item.
`.reduce(callback, initial?)`	`any`	Folds the items into one value: (acc, item, index) => ….
`.flatMap(callback)`	`array`	Maps, then flattens one level.
`.includes(value)`	`boolean`	True when the array contains the value (===).
`.indexOf(value)`	`number`	First index of the value, or -1.
`.lastIndexOf(value)`	`number`	Last index of the value, or -1.
`.join(separator?)`	`string`	Joins the items into a string (default ,).
`.slice(start?, end?)`	`array`	Part of the array (negative indexes count from the end).
`.concat(...values)`	`array`	New array with the values appended (arrays flattened one level).
`.at(index)`	`any`	Item at an index (negative counts from the end).
`.flat(depth?)`	`array`	Flattens nested arrays (default depth 1, max 10).
`.reverse()`	`array`	Reversed copy (the original never changes).
`.sort(compare?)`	`array`	Sorted copy (the original never changes). Without a comparator, sorts as strings like JS.

Number methods

Method	Returns	Description
`.toFixed(digits?)`	`string`	Fixed-point notation (0–100 digits).
`.toPrecision(precision)`	`string`	Significant-digit notation (1–100).
`.toString(radix?)`	`string`	Text form, optionally in base 2–36.
`.toLocaleString(locale?)`	`string`	Locale-formatted number (default: site locale).
`.toString()`	`string`	"true" or "false".