A single calendar month, optimized for a given locale
Demo: A default representation for the current month in browser's default locale


Given a reference date property, this component will show a calendar representation of that month. To the extent possible, this representation is sensitive to a specified locale: the names of the months and days of the week will be in the appropriate language, and the day(s) associated with the weekend in that locale will also be indicated.

The core grid of dates in CalendarMonth is provided by CalendarDays. To this, the component adds instances of CalendarMonthYearHeader and CalendarDayNamesHeader.

International support

All of the Elix calendar components attempt to provide full international support to the extent currently possible in the user's web browser. This includes being able to automatically show localized text strings for the desired language, as well as applying the desired region's cultural preferences for calendar layout.

Demo: English/U.S.: Weeks start on Sunday
Demo: English/Great Britain: Weeks start on Monday
Demo: French/France: Month and day names in French
Demo: Japanese/Japan: Month and day names in Japanese
Demo: Arabic/Kuwait: Weeks start on Saturday, weekend is Friday–Saturday
Demo: Hindi/India: Weekend is just Sunday

The precise set of supported locales may vary from browser to browser.

Demo: Calendars for the locales your browser supports


Like all complex Elix components, CalendarMonth and its associated calendar components can be extensively customized.

Demo: CalendarMonth showing custom data: here, the phase of the moon

The above calendar has been customized by defining a custom element that extends CalendarDay to show the phase of the moon on that day. This custom element is then used to fill the Day role on CalendarMonth. CalendarMonth will instantiate that custom element class for each day of the month and pass in the date that the element should show. The custom element can then perform whatever calculations and rendering logic it needs to show the appropriate data for that date.

You can also apply style the internal parts of a CalendarMonth to change its appearance directly with CSS:

Demo: CalendarMonth with CSS part styling

Note: As of November 2019, the above demo requires a pre-release version of Chrome or Edge to completely style the calendar's internal parts; you will also need to enable experimental web platform features by opening chrome://flags/#enable-experimental-web-platform-features. The demo will show partially-customized parts in production Chrome or pre-release versions of Firefox and Safari.


Class hierarchy:

The element defines the following shadow parts:

  • day: any of the day elements in the month grid, default type is CalendarDay
  • day-name: any of the names for the days of the week
  • day-names-header: the column header showing the names of the days, default type is CalendarDayNamesHeader
  • month-days: the grid of days for the month, default type is CalendarDays
  • month-year-header: the calendar header showing the month and/or year, default type is CalendarMonthYearHeader

booleanAttributeValue(name, value) static method

Given a string value for a named boolean attribute, return true if the value is either: a) the empty string, or b) a case-insensitive match for the name.

This is native HTML behavior; see the MDN documentation on boolean attributes for the reasoning.

Given a null value, this return false. Given a boolean value, this return the value as is.


  • name: string
  • value: string|boolean|null

Defined by AttributeMarshallingMixin

date property

The date that should be shown by the element. For elements that show a range of dates (a month, a week, etc.), the referenced date will be included in the range.

This property can be set as a string, which will be parsed and converted to a JavaScript Date.

If not specified, the default date value is the current date.

Type: Date

Defined by CalendarElementMixin

datechange event

Raised when the date property changes.

Defined by CalendarElementMixin

dayElementForDate(date) method

Returns the day element corresponding to the given date, or null if the date falls outside the range currently covered by this calendar.


  • date: Datethe date to search for

Returns: Elementnull

dayNamesHeaderPartType property

The class or tag used to create the header showing the day names.

Type: (component class constructor)|HTMLTemplateElement|string

Default: CalendarDayNamesHeader

dayPartType property

The class or tag used to create the day parts – the set of days shown in the calendar grid.

Type: (component class constructor)|HTMLTemplateElement|string

Default: CalendarDay

days property

Returns the day elements contained by this calendar. Note that this may include days from the previous/next month that fall in the same week as the first/last day of the present month.

Type: Array.

daysOfWeekFormat property

The format used to render the day names in the week days header.

The allowable formats are the same as the weekday formats in Intl.DateTimeFormat.

Type: 'long'|'narrow'|'short'

Default: 'short'

defaultState property

The default state for the component. This can be extended by mixins and classes to provide additional default state.

Type: PlainObject

Defined by ReactiveMixin

ids property

A convenient shortcut for looking up an element by ID in the component's Shadow DOM subtree.

Example: if component's template contains a shadow element <button id="foo">, you can use the reference this[ids].foo to obtain the corresponding button in the component instance's shadow tree. The ids property is simply a shorthand for getElementById, so this[ids].foo is the same as this[shadowRoot].getElementById('foo').

Type: object

Defined by ShadowTemplateMixin

locale property

A string that identifies a language and a region using a BCP 47 language tag. This is the same format used by to identify a locale in the standard Intl internationalization API. See the locales argument documentation for details.

Calendar elements are region-sensitive, so language alone is insufficient. Accordingly, the locale should identify at least a language and a region. Examples: "en-US" identifies US English, while "en-GB" identifies English in Great Britain. The use of "en" on its own would be insufficient.

Type: string

Defined by CalendarElementMixin

monthDaysPartType property

The class or tag used to create the grid of days.

Type: (component class constructor)|HTMLTemplateElement|string

Default: CalendarDays

monthFormat property

The format used to render the month name.

The allowable formats are the same as the month formats in Intl.DateTimeFormat.

Type: 'numeric'|'2-digit'|'long'|'short'|'narrow'

Default: 'long'

monthYearHeaderPartType property

The class or tag used to create the header showing the month and year.

Type: (component class constructor)|HTMLTemplateElement|string

Default: CalendarMonthYearHeader

render(changed) method

Render the indicated changes in state to the DOM.

The default implementation of this method does nothing. Override this method in your component to update your component's host element and any shadow elements to reflect the component's new state. See the rendering example.

Be sure to call super in your method implementation so that your component's base classes and mixins have a chance to perform their own render work.


  • changed: ChangedFlagsdictionary of flags indicating which state members have changed since the last render

Defined by ReactiveMixin

renderChanges() method

Render any pending component changes to the DOM.

This method does nothing if the state has not changed since the last render call.

ReactiveMixin will invoke this method following a setState call; you should not need to invoke this method yourself.

This method invokes the internal render method, then invokes the rendered method.

Defined by ReactiveMixin

rendered(changed) method

Perform any work that must happen after state changes have been rendered to the DOM.

The default implementation of this method does nothing. Override this method in your component to perform work that requires the component to be fully rendered, such as setting focus on a shadow element or inspecting the computed style of an element. If such work should result in a change in component state, you can safely call setState during the rendered method.

Be sure to call super in your method implementation so that your component's base classes and mixins have a chance to perform their own post-render work.


  • changed: ChangedFlags

Defined by ReactiveMixin

setState(changes) method

Update the component's state by merging the specified changes on top of the existing state. If the component is connected to the document, and the new state has changed, this returns a promise to asynchronously render the component. Otherwise, this returns a resolved promise.


  • changes: PlainObjectthe changes to apply to the element's state

Returns: Promise - resolves when the new state has been rendered

Defined by ReactiveMixin

state property

The component's current state.

The returned state object is immutable. To update it, invoke internal.setState.

It's extremely useful to be able to inspect component state while debugging. If you append ?elixdebug=true to a page's URL, then ReactiveMixin will conditionally expose a public state property that returns the component's state. You can then access the state in your browser's debug console.

Type: PlainObject

Defined by ReactiveMixin

stateEffects(state, changed) method

Ask the component whether a state with a set of recently-changed fields implies that additional second-order changes should be applied to that state to make it consistent.

This method is invoked during a call to internal.setState to give all of a component's mixins and classes a chance to respond to changes in state. If one mixin/class updates state that it controls, another mixin/class may want to respond by updating some other state member that it controls.

This method should return a dictionary of changes that should be applied to the state. If the dictionary object is not empty, the internal.setState method will apply the changes to the state, and invoke this stateEffects method again to determine whether there are any third-order effects that should be applied. This process repeats until all mixins/classes report that they have no additional changes to make.

See an example of how ReactiveMixin invokes the stateEffects to ensure state consistency.


  • state: PlainObjecta proposal for a new state
  • changed: ChangedFlagsthe set of fields changed in this latest proposal for the new state

Returns: PlainObject

Defined by ReactiveMixin

yearFormat property

The format used to render the year.

The allowable formats are the same as the year formats in Intl.DateTimeFormat.

Type: 'numeric'|'2-digit'

Default: 'numeric'