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JS Reference

JS by Category JS by Alphabet

JavaScript

JS Arrays
Array[ ] Array( ) at() concat() constructor copyWithin() entries() every() fill() filter() find() findIndex() findLast() findLastIndex() flat() flatMap() forEach() from() includes() indexOf() isArray() join() keys() lastIndexOf() length map() of() pop() prototype push() reduce() reduceRight() rest (...) reverse() shift() slice() some() sort() splice() spread (...) toReversed() toSorted() toSpliced() toString() unshift() values() valueOf() with()
JS Boolean
Boolean() new Boolean() constructor prototype toString() valueOf()
JS Classes
constructor() extends static super
JS Dates
new Date() constructor getDate() getDay() getFullYear() getHours() getMilliseconds() getMinutes() getMonth() getSeconds() getTime() getTimezoneOffset() getUTCDate() getUTCDay() getUTCFullYear() getUTCHours() getUTCMilliseconds() getUTCMinutes() getUTCMonth() getUTCSeconds() now() parse() prototype setDate() setFullYear() setHours() setMilliseconds() setMinutes() setMonth() setSeconds() setTime() setUTCDate() setUTCFullYear() setUTCHours() setUTCMilliseconds() setUTCMinutes() setUTCMonth() setUTCSeconds() toDateString() toISOString() toJSON() toLocaleDateString() toLocaleTimeString() toLocaleString() toString() toTimeString() toUTCString() UTC() valueOf()
JS Function
Function apply() Function bind() Function call() Function length Function name Function toString() Function valueOf()
JS Error
new Error() cause isError() name message
JS Global
decodeURI() decodeURIComponent() encodeURI() encodeURIComponent() escape() eval() Infinity isFinite() isNaN() NaN Number() parseFloat() parseInt() String() undefined unescape()
JS Intl Namespace JS Iterators
drop() every() filter() find() flatMap() forEach() from() map() reduce() some() take()
JS JSON
parse() stringify()
JS Maps
new Map clear() delete() entries() forEach() get() groupBy() has() keys() set() size values()
JS Math
abs() acos() acosh() asin() asinh() atan() atan2() atanh() cbrt() ceil() clz32() cos() cosh() E exp() expm1() f16round() floor() fround() LN2 LN10 log() log10() log1p() log2() LOG2E LOG10E max() min() PI pow() random() round() sign() sin() sinh() sqrt() SQRT1_2 SQRT2 tan() tanh() trunc()
JS Numbers
constructor EPSILON isFinite() isInteger() isNaN() isSafeInteger() MAX_SAFE_INTEGER MIN_SAFE_INTEGER MAX_VALUE MIN_VALUE NaN NEGATIVE_INFINITY POSITIVE_INFINITY parseFloat() parseInt() prototype toExponential() toFixed() toLocaleString() toPrecision() toString() valueOf()
JS Objects
assign() constructor create() defineProperties() defineProperty() delete entries() freeze() fromEntries() getOwnPropertyDescriptor() getOwnPropertyDescriptors() getOwnPropertyNames() groupBy() isExtensible() isFrozen() isSealed() keys() preventExtensions() prototype seal() toString() valueOf() values()
JS Operators JS Assignment
Assign Simple Assign Add Assign Subtract Assign Multiply Assign Divide Assign Remainder Assign Colon Assign AND Assign OR Assign Nullish
JS Arithmetic
Addition Subtraction Multiplication Division Exponentiation Remainder Increment Decrement Concatenation Unary Plus Unary Negation
JS Comparison
Equal Strict Equal Not Equal Strict Not Equal Greater Than Less Than Greater Equal Less Equal
JS Logical Operators
Logical AND Logical OR Logical NOT Logical Nullish
JS Bitwise Operators
Bitwise AND Bitwise OR Bitwise NOT Bitwise XOR Bitwise Left Bitwise Right Bitwise Signed
JS Misc Operators
: ?. ... () ? x : y => delete in instanceof typeof void
JS Precedence JS Promises
all() allSettled() any() catch() finally() race() reject() resolve() then() try() withResolvers()
JS Proxy
apply() construct() defineProperty() deleteProperty() get() getOwnPropertyDescriptor() getPrototypeOf() has() isExtensible() ownKeys() preventExtentions() set() setPrototypeOf()
JS Reflect
apply() construct() defineProperty() deleteProperty() get() getOwnPropertyDescriptor() getPrototypeOf() has() isExtensible() ownKeys() preventExtentions() set() setPrototypeOf()
JS RegExp Patterns
/d /g /i /m /s /u /v /y [a] [^a] [abc] [^abc] [A-Z] [^A-Z] [0-9] [^0-9] a|b . \w \W \d \D \s \S [\b] \0 \n \f \r \t \v \p \P \ddd \xhh \uhhhh ^ $ \b \B x(?=y) x(?!y) (?<=y)x (?<!y)x (x) (?<name>x) (?flags:x) + * ? {n} {n,m} {n,}
JS RegExp Reference
compile() constructor dotAll escape() exec() flags global hasIndices ignoreCase lastIndex multiline source sticky test() toString() unicode unicodeSets
JS Sets
new Set add() clear() delete() difference() entries() forEach() has() intersection() isDisjointFrom() isSubsetOf() isSupersetOf() keys() size symmetricDifference() union() values()
JS Statements
break class const continue debugger do...while for for...in for...of function if...else let return switch throw try...catch var while
JS Strings
at() charAt() charCodeAt() codePointAt() concat() constructor endsWith() fromCharCode() includes() indexOf() isWellFormed() lastIndexOf() length localeCompare() match() matchAll() padEnd() padStart() prototype repeat() replace() replaceAll() search() slice() split() startsWith() substr() substring() toLocaleLowerCase() toLocaleUpperCase() toLowerCase() toString() toUpperCase() toWellFormed() trim() trimEnd() trimStart() valueOf()
JS Typed Arrays
Int8Array Uint8Array Uint8ClampedArray Int16Array Uint16Array Int32Array Uint32Array BigInt64Array BigUint64Array Float16Array Float32Array Float64Array
JS Typed Reference
at() byteLength byteOffset bytesPerElement copyWithin() entries() every() fill() filter() find() findIndex() findLast() findLastIndex() forEach() from() includes() indexOf() join() keys() lastIndexOf() length map() name of() reduce() reduceRight() reverse() set() slice() some() sort() subarray() toLocaleString() toReversed() toSorted() toString() values() with()

Temporal

Temporal Objects New Temporal.Duration
abs() add() compare() from() negated() new (constructor) round() subtract() toJSON() toLocaleString() toString() total() valueOf() with()
Temporal.Instant
add() compare() equals() from() fromEpochMilliseconds() fromEpochNanoseconds() new (constructor) round() since() subtract() toJSON() toLocaleString() toString() toZonedDateTimeISO() until() valueOf()
Temporal.Now
instant() plainDateISO() plainDateTimeISO() plainTimeISO() timeZoneId() zonedDateTimeISO()
Temporal.PlainDate
add() compare() equals() from() new (constructor) since() subtract() toJSON() toLocaleString() toPlainDateTime() toPlainMonthDay() toPlainYearMonth() toString() toZonedDateTime() until() valueOf() with() withCalendar()
Temporal.PlainDateTime
add() compare() equals() from() new (constructor) round() since() subtract() toJSON() toLocaleString() toPlainDate() toPlainTime() toString() toZonedDateTime() until() valueOf() with() withCalendar() withPlainTime()
Temporal.PlainMonthDay
equals() from() new (constructor) toJSON() toLocaleString() toPlainDate() toString() valueOf() with()
Temporal.PlainTime
add() compare() equals() from() new (constructor) round() since() subtract() toJSON() toLocaleString() toString() until() valueOf() with()
Temporal.PlainYearMonth
add() compare() equals() from() new (constructor) since() subtract() toJSON() toLocaleString() toPlaindate() toString() until() valueOf() with()
Temporal.ZonedDate
add() compare() equals() from() getTimeZonetransition() new() round() since() startofday() subtract() toInstant() toJSON() toLocaleString() toPlainDate() toPlainDateTime() toPlainTime() toString() until() valueOf() with() withCalendar() withPlainTime() withTimeZone()

Window

Window Object
addeventlistener() alert() atob() blur() btoa() clearInterval() clearTimeout() close() closed confirm() console defaultStatus document focus() frameElement frames history getComputedStyle() innerHeight innerWidth length localStorage location matchMedia() moveBy() moveTo() name navigator open() opener outerHeight outerWidth pageXOffset pageYOffset parent print() prompt() removeEventlistener() resizeBy() resizeTo() screen screenLeft screenTop screenX screenY scrollBy() scrollTo() scrollX scrollY sessionStorage self setInterval() setTimeout() status stop() top
Window Console
assert() clear() count() dir() error() group() groupCollapsed() groupEnd() info() log() table() time() timeEnd() trace() warn()
Window History
back() forward() go() length
Window Location
assign() hash host hostname href origin pathname port protocol reload() replace() search
Window Navigator
appCodeName appName appVersion cookieEnabled geolocation javaEnabled() language onLine platform product taintEnabled() userAgent
Window Screen
availHeight availWidth colorDepth height pixelDepth width

HTML DOM

HTML Documents
activeElement addEventListener() adoptNode() anchors applets baseURI body charset characterSet close() cookie createAttribute() createComment() createDocumentFragment() createElement() createEvent() createTextNode() defaultView designMode doctype documentElement documentMode documentURI domain domConfig embeds execCommand() forms getElementById() getElementsByClassName() getElementsByName() getElementsByTagName() hasFocus() head images implementation importNode() inputEncoding lastModified links normalize() normalizeDocument() open() querySelector() querySelectorAll() readyState referrer removeEventListener() renameNode() scripts strictErrorChecking title URL write() writeln()
HTML Elements
accessKey addEventListener() after() append() appendChild() attributes before() blur() childElementCount childNodes children classList className click() clientHeight clientLeft clientTop clientWidth cloneNode() closest() compareDocumentPosition() contains() contentEditable dir firstChild firstElementChild focus() getAttribute() getAttributeNode() getBoundingClientRect() getElementsByClassName() getElementsByTagName() hasAttribute() hasAttributes() hasChildNodes() id innerHTML innerText insertAdjacentElement() insertAdjacentHTML() insertAdjacentText() insertBefore() isContentEditable isDefaultNamespace() isEqualNode() isSameNode() isSupported() lang lastChild lastElementChild matches() namespaceURI nextSibling nextElementSibling nodeName nodeType nodeValue normalize() offsetHeight offsetWidth offsetLeft offsetParent offsetTop outerHTML outerText ownerDocument parentNode parentElement previousSibling previousElementSibling querySelector() querySelectorAll() remove() removeAttribute() removeAttributeNode() removeChild() removeEventListener() replaceChild() scrollHeight scrollIntoView() scrollLeft scrollTop scrollWidth setAttribute() setAttributeNode() style tabIndex tagName textContent title
HTML Attributes
getNamedItem() isId item() length name removeNamedItem() setNamedItem() specified value
HTML Collection
item() length namedItem()
HTML NodeList
entries() forEach() item() keys() length values()
HTML DOMTokenList
add() contains() entries() forEach() item() keys() length remove() replace() supports() toggle() value values()
HTML Styles
alignContent alignItems alignSelf animation animationDelay animationDirection animationDuration animationFillMode animationIterationCount animationName animationTimingFunction animationPlayState background backgroundAttachment backgroundClip backgroundColor backgroundImage backgroundOrigin backgroundPosition backgroundRepeat backgroundSize backfaceVisibility border borderBottom borderBottomColor borderBottomLeftRadius borderBottomRightRadius borderBottomStyle borderBottomWidth borderCollapse borderColor borderImage borderImageOutset borderImageRepeat borderImageSlice borderImageSource borderImageWidth borderLeft borderLeftColor borderLeftStyle borderLeftWidth borderRadius borderRight borderRightColor borderRightStyle borderRightWidth borderSpacing borderStyle borderTop borderTopColor borderTopLeftRadius borderTopRightRadius borderTopStyle borderTopWidth borderWidth bottom boxShadow boxSizing captionSide caretColor clear clip color columnCount columnFill columnGap columnRule columnRuleColor columnRuleStyle columnRuleWidth columns columnSpan columnWidth counterIncrement counterReset cssFloat cursor direction display emptyCells filter flex flexBasis flexDirection flexFlow flexGrow flexShrink flexWrap font fontFamily fontSize fontStyle fontVariant fontWeight fontSizeAdjust height isolation justifyContent left letterSpacing lineHeight listStyle listStyleImage listStylePosition listStyleType margin marginBottom marginLeft marginRight marginTop maxHeight maxWidth minHeight minWidth objectFit objectPosition opacity order orphans outline outlineColor outlineOffset outlineStyle outlineWidth overflow overflowX overflowY padding paddingBottom paddingLeft paddingRight paddingTop pageBreakAfter pageBreakBefore pageBreakInside perspective perspectiveOrigin position quotes resize right scrollBehavior tableLayout tabSize textAlign textAlignLast textDecoration textDecorationColor textDecorationLine textDecorationStyle textIndent textOverflow textShadow textTransform top transform transformOrigin transformStyle transition transitionProperty transitionDuration transitionTimingFunction transitionDelay unicodeBidi userSelect verticalAlign visibility width wordBreak wordSpacing wordWrap widows zIndex

HTML Events

HTML Events
abort afterprint animationend animationiteration animationstart beforeprint beforeunload blur canplay canplaythrough change click contextmenu copy cut dblclick drag dragend dragenter dragleave dragover dragstart drop durationchange ended error focus focusin focusout fullscreenchange fullscreenerror hashchange input invalid keydown keypress keyup load loadeddata loadedmetadata loadstart message mousedown mouseenter mouseleave mousemove mouseover mouseout mouseup offline online open pagehide pageshow paste pause play playing progress ratechange resize reset scroll search seeked seeking select show stalled submit suspend timeupdate toggle touchcancel touchend touchmove touchstart transitionend unload volumechange waiting wheel
HTML Event Objects
Animation Events Clipboard Events Drag Events Events Focus Events HashChange Events Input Events Keyboard Events Mouse Events PageTransition Events PopState Events Progress Events Storage Events Touch Events Transition Events Ui Events Wheel Events
HTML Event Properties
altKey (Mouse) altKey (Key) animationName bubbles button buttons cancelable charCode clientX clientY code ctrlKey (Mouse) ctrlKey (Key) currentTarget data defaultPrevented deltaX deltaY deltaZ deltaMode detail elapsedTime elapsedTime eventPhase inputType isTrusted key keyCode location metaKey (Mouse) metaKey (Key) newURL oldURL offsetX offsetY pageX pageY persisted propertyName relatedTarget relatedTarget screenX screenY shiftKey (Mouse) shiftKey (Key) target targetTouches timeStamp touches type which (Mouse) which (Key) view
HTML Event Methods
getModifierState() preventDefault() stopImmidiatePropagation() stopPropagation()

Web APIs

API Canvas API Console API Fetch API Fullscreen
exitFullscreen() fullscreenElement fullscreenEnabled() requestFullscreen()
API Geolocation
coordinates getCurrentPosition() position
API History API MediaQueryList API Storage
clear() getItem() key() length removeItem() setItem()
API Validation API Web
crypto.getRandomNumber()

HTML Objects

<a> <abbr> <address> <area> <article> <aside> <audio> <b> <base> <bdo> <blockquote> <body> <br> <button> <canvas> <caption> <cite> <code> <col> <colgroup> <datalist> <dd> <del> <details> <dfn> <dialog> <div> <dl> <dt> <em> <embed> <fieldset> <figcaption> <figure> <footer> <form> <head> <header> <h1> - <h6> <hr> <html> <i> <iframe> <img> <ins> <input> button <input> checkbox <input> color <input> date <input> datetime <input> datetime-local <input> email <input> file <input> hidden <input> image <input> month <input> number <input> password <input> radio <input> range <input> reset <input> search <input> submit <input> text <input> time <input> url <input> week <kbd> <label> <legend> <li> <link> <map> <mark> <menu> <menuitem> <meta> <meter> <nav> <object> <ol> <optgroup> <option> <output> <p> <param> <pre> <progress> <q> <s> <samp> <script> <section> <select> <small> <source> <span> <strong> <style> <sub> <summary> <sup> <table> <tbody> <td> <tfoot> <th> <thead> <tr> <textarea> <time> <title> <track> <u> <ul> <var> <video>

Other References

CSSStyleDeclaration
cssText getPropertyPriority() getPropertyValue() item() length parentRule removeProperty() setProperty()
JS Conversion


ZonedDateTime startOfDay()

❮ Previous ZonedDateTime Reference Next ❯

Example

const zoned = Temporal.PlainDateTime.from("2026-05-17T14:30:00");

const start = zoned.startOfDay();
Try it Yourself »

Description

The startOfDay() method returns a Temporal.ZonedDateTime object representing the first instant of this date in the time zone.

The startOfDay() method does not change the original ZonedDateTime object.

Syntax

zoneddatetime.startOfDay()

Parameters

NONE

Return Value

Type Description
Objecta Temporal.ZonedDateTime object representing the first instant of this date in the time zone.

Browser Support

Temporal is a major update to the JavaScript standard (TC39).

It is currently supported in Chrome, Edge, Firefox, and Opera and is expected to reach full availability across browsers before the summer of 2026.

Chrome
144		 Edge
144		 Firefox
139		 Safari
 Opera
128
Jan 2026 Jan 2026 May 2025 🚫 Feb 2026

The Safari implementation can be tested in Safari Technology Preview by enabling the --use-temporal runtime flag.

Polyfill

Until Safari support Temporal natively, you can use the official polyfill:

<script
src="https://cdn.jsdelivr.net/npm/@js-temporal/polyfill/dist/index.umd.js">
</script>

❮ Previous ZonedDateTime Reference Next ❯
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