Built-ins

Every function, browser value, method and global the language gives a program, in one place.

Functions

Functions
Function Does Where

log(x, …)

 Prints to the console anywhere

navigate(path)

 Moves to a route; in a static build, a page load actions, handlers

format(value, .style, option)

 A number, date or money as text, in the locale

anywhere (chapter 14)

ago(date)

 "3 minutes ago", "in 2 days" anywhere

t("key", { name: value })

 A translation, with placeholders and plurals

anywhere (chapter 21)

setLocale("ar")

 Switches the locale, and the direction with it actions, handlers, effects

setTheme("dark")

"light", "dark" or "system", kept across visits

 actions, handlers

uuid()

A fresh Uuid

 anywhere

sanitize(html)

Markup through an allow-list, for Unsafe.Html

anywhere (chapter 23)

fetch(url, options)

A request through the same engine as api; await it

actions (chapter 17)

optimistic(holder, change)

 Shows a change now, takes it back if the action throws

actions (chapter 17)

beacon(url, data)

 A small post that survives the page unloading

anywhere (chapter 18)

animate(element, name, duration)

 Plays an animation on a handle

handlers (chapter 20)

replayAnimation(element, name)

 Plays an element's own animation again handlers

every(interval) { }, after(interval) { }

 A repeating and a one-off timer, stopped when their scope leaves

render blocks (chapter 8)

ws(url), sse(url), broadcast(name), rtc(signal: …)

Open a socket, a stream, a channel, a peer — after socket x =, stream x =, channel x =, peer x =

render blocks (chapter 18)

Browser values

Always in scope and kept current; a state of the same name shadows one.

Browser values
Name Holds

viewport

.width, .height, .sm, .md, .lg, .xl

query

 the query string, as a map

hash

the fragment, without #

theme

"light", "dark" or "system"

now

the current DateTime, every minute; now(every: 1.seconds)

network

.online, .effectiveType, .saveData, .downlink, .queued

update

.available, .apply() — a new version of an offline site

locale, dir

 the current locale and direction, with i18n configured

params

 the route's parameters, by name

String methods

length, trim(), trimStart(), trimEnd(), toLowerCase(), toUpperCase(), includes(s), startsWith(s), endsWith(s), indexOf(s), lastIndexOf(s), slice(a, b), substring(a, b), charAt(i), at(i), replace(a, b), replaceAll(a, b), split(sep), padStart(n, c), padEnd(n, c), repeat(n), normalize(), localeCompare(other), match(re), search(re) — the browser's — and WebFluent's own:

String methods
Method Gives

capitalize()

 The first letter in upper case

truncate(n)

At most n characters, with … when cut

dedent()

 The text without the indentation its lines share

lines()

 A list of its lines

words()

 A list of its words, split on whitespace

List methods

length, map(f), filter(f), find(f), findIndex(f), some(f), every(f), includes(x), indexOf(x), reduce(f, init), join(sep), slice(a, b), concat(other), reverse(), sort(f), flatMap(f) — the browser's; push(x) in an action — and WebFluent's own:

List methods
Method Gives

sortBy(f)

A sorted copy, by what f returns

groupBy(f)

A map from what f returns to the items that returned it

unique()

 A copy without repeats

take(n)

The first n items

first(), last()

The first or last item, or null

sum()

 The total of a list of numbers

Every helper runs at build time too, so a static page shows its result.

Number methods

toFixed(n), toString(). Convert with Number("12") and String(n), or "{n}"; round with Math.round, Math.floor, Math.max and the rest.

The built-in types

The built-in types
Type Written Methods and fields

Date

@2026-03-14

.year() .month() .day() .weekday(), .plus(days: 3), .minus(…), .isBefore(d) .isAfter(d) .isSame(d), .until(d), .startOfDay() .startOfWeek() .startOfMonth() .endOfDay(), .native()

Time

@09:30

.hour() .minute() .second(), .plus(minutes: 30), the comparisons

DateTime

@2026-03-14T09:30Z

the above, .date() .time(), .inZone("Europe/Berlin")

Duration

90.minutes, 3.days, 250.ms

.days() .hours() .minutes() .seconds() .ms(), .plus(d)

Money

€12.99, $9.99, £4.50

.plus(m) .minus(m) .times(n) .convert(rate, "USD"), .amount, .currency

Url

 a string

.host() .path() .query(), .with(query: { page: 2 })

Email

 a string

.domain()

Color

#0F766E

.mix(other, 0.2) .lighten(n) .darken(n) .alpha(0.5) .contrast(other)

Uuid

uuid()

 a string's

File

from FileUpload

.preview(), .name, .size, .type

Secret

 — none: it may not be shown, spliced, logged or persisted

.plus and .minus take years, months, weeks, days, hours, minutes, seconds and ms. Durations are written with ms, seconds, minutes, hours, days and weeks. Chapter 13 has the rest.

Browser globals

These compile to themselves, with no prefix: window, document, console, navigator, location, localStorage, sessionStorage, JSON, Math, Date, setTimeout, setInterval, clearTimeout, clearInterval, parseInt, parseFloat, Array, Object, String, Number, Boolean, Promise, Error, Map, Set, RegExp, Infinity, NaN, undefined, encodeURIComponent, decodeURIComponent, encodeURI, decodeURI, atob, btoa, alert, confirm, prompt, requestAnimationFrame, cancelAnimationFrame, history, screen, performance, crypto, globalThis, Intl, Symbol, Reflect, URL, URLSearchParams, FormData, Blob, File, FileReader, Event, CustomEvent, AbortController, TextEncoder, TextDecoder, Notification, matchMedia, getComputedStyle, structuredClone, queueMicrotask. The checker types them as Any, and a name the program declares itself wins over them.