Renderables

Renderables or components are the building blocks of Tempo applications. They are the templates that are rendered to the DOM. Tempo provides a set of functions to create and manipulate renderables.

The Renderable functions use the convention of starting with a capital letter. This is to differentiate them from regular functions and to make it easier to identify them in the code. The notable exception is for basic html/svg elements, which are lowercase.

HTML/SVG, text and Attributes

To create HTML or SVG elements, use the html and svg objects. Each of them contains the full list of available tags as functions. For example, to create a div element, use html.div(). To create a circle element, use svg.circle().

These functions take an arbitrary number of TNode arguments. A TNode can be a string, a Signal, a Renderable, a Renderable[] or null/undefined.

To create text nodes, you can just pass a string or a Signal where a TNode is expected. Alternatively you can be explicit and use the TextNode() function.

const titleSignal = signal('Hello, World!')

html.div(
  'Hello, World!', // <-- this is a text node
  titleSignal, // <-- this is a signal that automatically updates a text node
  html.span('This is a span'),
  TextNode('This is also a text node')
)

To create DOM attributes and properties use the attr object. It contains functions for all the standard attributes and properties. For example, to set the id attribute, use attr.id('my-id').

html.image(
  attr.id('my-id'),
  attr.src('https://example.com/image.jpg'),
  attr.title(titleSignal)
)

You will have noticed that text nodes and attribute values accept both literal values (ex. 'Hello, World!') and signals (ex. titleSignal). This is because the arguments are typed as Value which is a union of T and Signal. Value also happens to be part of the TNode union.

attr.class

The class attribute is special in the sense that can be used multiple times in the same element.

const classSignal = signal('class3 class4')
html.div(
  attr.class('class1 class2'),
  attr.class(classSignal)
)

A class attribute can be a string or a signal that emits a string. The string can contain multiple classes separated by spaces.

Other attributes and elements

There are helper objects to create arbitrary data-attributes, math/svg elements and attributes, and style attributes.

html.div(
  dataAttr.mydata('myvalue'),
  math.math(
    mathAttr.display('inline'),
    math.mfrac(
      math.msup(
        math.mi('π'),
        math.mn('2'),
      ),
      math.mn('6'),
    ),
  ),
  svg.svg(
    svg.circle(svgAttr.cx(50), svgAttr.cy(50), svgAttr.r(40)),
  ),
  style.color('red')
)

Events

Similar to attributes, events can be set using the on object. The on object contains functions for all the standard events. For example, to set the click event, use on.click(fn).

It is fine to use signal.value or signal.get() to get the value of a signal in an event handler.

emit

Tempo provides a set of functions to simplify event handling. For example emitValue emits the value of the current input element when the event is triggered.

input elements

When using input elements it is very common you want to specify the type of the input. Tempo provides a set of functions to create input elements with the correct type. For example, to create a number input, use input.number().

bind

Tempo provides functions to bind Props to input elements. For example, to bind a string prop to an input element, use bindText. This sets a bidirectional binding between the prop and the input element.

Conditionals

Tempo has a set of functions to create conditional renderables. For example, to render a div element only if a condition is met, use When (or Unless for its negation).

const showSignal = makeSignal(true)

When(showSignal,
  html.div('This is visible')
)

A second argument can be passed to When to specify a renderable to show when the condition is false.

An interesting aspect of conditionals in Tempo, is that there is no DOM rebuilding unless the branch is changed.

Ensure

In TypeScript it is common to work with values that can be null or undefined. To render a value only if it is not null or undefined, use Ensure.

const valueSignal = makeSignal<string | null>('Hello, World!')

Ensure(
  valueSignal,
  v => html.div(v.map(text => `This is visible: ${text}`))
)

Unlike When, Ensure takes a function that returns a renderable. This function is called with a new signal that is guaranteed to be not null or undefined.

OneOf

For more complicated pattern matching you can use one of the OneOf renderables. You generally match on the value of an object field. For that you can use OneOfField, OneOfKind, or OneOfType.

type MyType = { kind: 'A', text: string } | { kind: 'B', value: number }

const valueSignal = makeSignal<MyType>({ kind: 'A', text: 'Hello, World!' })

OneOfKind(valueSignal, {
  A: v => html.div('A: ', v.$.text),
  B: v => html.div('B: ', v.$.value.map(String))
})

Loops

Of course you can also render lists of elements. Tempo provides a set of functions to create loops. For example, to render a list of div elements, use ForEach.

const itemsSignal = makeSignal(['Item 1', 'Item 2', 'Item 3'])

ForEach(
  itemsSignal,
  (item, position) => html.div(
    position.$.counter.map(String),
    ': ',
    item
  )
)

The renderable function takes two arguments. The first is a signal that represent an element of the list. The second is a signal that represents the position of the element in the list. The position signal has a counter field that is the 1-based index of the element in the list as well as a isFirst, isLast and index.

ForEach accepts an optional third argument to render a separator between elements.

You can wrap your loop in a NotEmpty renderable if you want to ensure that the list is not empty. This is useful in the case of structures like UL or OL where an empty list would not be desired.

const itemsSignal = makeSignal(['Item 1', 'Item 2', 'Item 3'])

NotEmpty(
  itemsSignal,
  items => html.ul(
    ForEach(
      items,
      item => html.li(item),
      html.br()
    ),
  ),
  () => 'No items'
)

Repeat takes a signal that represents the number of times to repeat the renderable. It is useful when you want to repeat a renderable a fixed number of times.

const countSignal = makeSignal(3)

Repeat(
  countSignal,
  pos => html.div(pos.$.counter.map(String))
)

If you know ahead of time the number and content of the elements, you can use a regular loop to create an array of renderables.

const items = ['Item 1', 'Item 2', 'Item 3']

html.div(
  items.map((item, index) => html.div(String(index), ': ', item))
)

Lifecycle

For more advanced use cases, Tempo provides a set of functions to handle the lifecycle of a renderable. For example, to run a function when a renderable is mounted, use OnMount. This will take a callback function that will be called with the HTML Dom Element just mounted. Similarly OnCtx will take a callback function that will be called with the current DOMContext.

html.div(
  // element is the DIV Element just mounted
  OnMount(element => {
    console.log('Mounted', element)
  })
)

Whenever you want to cleanup resources when a renderable is unmounted, use OnUnmount.

html.div(
  OnMount(element => {
    const listener = () => console.log('Clicked')
    element.addEventListener('click', listener)
    OnUnmount(removeTree => {
      if (removeTree) {
        element.removeEventListener('click', listener)
      }
    })
  })
)

Fragment/Empty

You can use Fragment where a single renderable is expected but you want to render multiple components. Similarly, you can use Empty to fill a slot with nothing.

Providers and Consumers

To simplify the structure of a larger project, it is often useful to use a Provider/Consumer pattern. In a high-level component, you can provide a value (or function, or signal, or anything really) that is consumed by a lower-level component. You can use WithProvider to provide a single value, and UseProvider to consume it.

They both required a ProviderMark to be passed as the first argument. This is a unique symbol that is used to identify the provider. You can use makeProviderMark to create a unique mark for your own provider/consumer.

type Preferences = Signal<{ theme: string }>
const PreferencesMark = makeProviderMark<Preferences>('Preferences')

const MyComponent = WithProvider(
  PreferencesMark,
  makeSignal({ theme: 'bubbly' }),
  html.div(
    UseProvider(PreferencesMark, value => html.div(value.$.theme))
  )
)

When creating reusable providers, you probably want to wrap them in a provider function. This function has generally the signature (node: TNode) => Renderable.

const PreferencesProvider = (node: TNode) => {
  const preferences = makeSignal<Preferences>({ theme: 'bubbly' })
  return WithProvider(
    PreferencesMark,
    preferences,
    node
  )
}

Similarly on the consumer side, you can have:

const UsePreferences = (fn: (preferences: Signal) => TNode) =>
  UseProvider(PreferencesMark, fn)

Now you can use them together for easy access to the preferences:

PreferencesProvider(
  html.div(
    UsePreferences(preferences => html.div(preferences.$.theme))
  )
)

Asynchrnous Operations

If you are dealing with asynchronous operations, you can use Async to render a promise or Task to render a function that returns a promise. More likely than not you will want to use a combination of Signals and Promise to define your UI. Let's take as an example loading from an API.

const dataSignal = Signal.ofPromise<string | null>(
  async () => {
    const res = await fetch('https://api.example.com/data')
    return r.text()
  },
  null // this is the default state before the promise resolves
)

html.div(
  Ensure(
    dataSignal,
    data => html.div(data),
    html.div('Loading...')
  )
)

Often you will want to refetch when some parameter changes.

const idSignal = makeSignal(1)

const dataSignal = idSignal.mapAsync<string | null>(
  async (id) => {
    const res = await fetch(`https://api.example.com/data/${id}`)
    return r.text()
  },
  null // this is the default state before the promise resolves
)

// the rest remains the same

Portal

A Portal is a way to render a renderable in a different part of the DOM. This is useful when you want to render a modal, a tooltip or you want to make changes to the head element. The HTMLTitle renderable defined in the @tempots/ui package is a good example of this.

export const HTMLTitle = (title: Value<string>) =>
  Portal('head > title', attr.innerText(title))

Next Steps

▾ on this page ▾

Renderables
HTML/SVG, text and Attributes
attr.class
Other attributes and elements
Events
emit
input elements
bind
Conditionals
Ensure
OneOf
Loops
Lifecycle
Fragment/Empty
Providers and Consumers
Asynchrnous Operations
Portal
Next Steps