lustre - v4.0.0-rc.2

lustre/element

Note: this is a release candidate for v4.0.0 and documentation is still a work in progress. If you spot an issue with docs or the library, or would like to get involved, please open an issue or a pull request.

Lustre wouldn’t be much use as a frontend framework if it didn’t provide a way to create HTML elements. This module contains the basic functions necessary to construct and manipulate different HTML elements.

It is also possible to use Lustre as a HTML templating library, without using its runtime or framework features.

Types

Element

</>

The Element type is how Lustre represents chunks of HTML. The msg type variable is used to represent the types of messages that can be produced from events on the element or its children.

Note: Just because an element can produces messages of a given type, doesn’t mean that it will! The msg type variable is used to represent the potential for messages to be produced, not a guarantee.

The most basic ways to create elements are:

  • The element function to construct arbitrary HTML elements. You can also use this render Custom Elements (like those registered as Lustre components).

  • The text function to turn a Gleam string into a text node.

  • The none function to render nothing - useful for conditional rendering.

If you have more complex needs, there are two more-advanced functions:

  • The namespaced function to create elements in a specific XML namespace. This is useful for SVG or MathML elements, for example.

  • The advanced function to create elements with more control over how the element is rendered when converted to a string. This is necessary because some HTML, SVG, and MathML elements are self-closing or void elements, and Lustre needs to know how to render them correctly!

For most applications, you’ll only need to use the simpler functions; usually the text and none functions are enough. This is because Lustre already provides a module with all the standard HTML and SVG elements ready to use in lustre/element/html and lustre/element/svg.

pub type Element(msg) =
  vdom.Element(msg)

Functions

advanced

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pub fn advanced(
  namespace: String,
  tag: String,
  attrs: List(Attribute(a)),
  children: List(Element(a)),
  self_closing: Bool,
  void: Bool,
) -> Element(a)

A function for constructing elements with more control over how the element is rendered when converted to a string. This is necessary because some HTML, SVG, and MathML elements are self-closing or void elements, and Lustre needs to know how to render them correctly!

element

</> 
pub fn element(
  tag: String,
  attrs: List(Attribute(a)),
  children: List(Element(a)),
) -> Element(a)

A general function for constructing any kind of element. In most cases you will want to use the lustre/element/html instead but this function is particularly handing when constructing custom elements, either from your own Lustre components or from external JavaScript libraries.

Note: Because Lustre is primarily used to create HTML, this function spcieal-cases the following tags render as void elements:

  • area
  • base
  • br
  • col
  • embed
  • hr
  • img
  • input
  • link
  • meta
  • param
  • source
  • track
  • wbr

This will only affect the output of to_string and to_string_builder! If you need to render any of these tags with children, or you want to render some other tag as self-closing or void, use advanced to construct the element instead.

map

</> 
pub fn map(element: Element(a), f: fn(a) -> b) -> Element(b)

The Element type is parameterised by the type of messages it can produce from events. Sometimes you might end up with a fragment of HTML from another library or module that produces a different type of message: this function lets you map the messages produced from one type to another.

Think of it like list.map or result.map but for HTML events!

namespaced

</> 
pub fn namespaced(
  namespace: String,
  tag: String,
  attrs: List(Attribute(a)),
  children: List(Element(a)),
) -> Element(a)

A function for constructing elements in a specific XML namespace. This can be used to construct SVG or MathML elements, for example.

none

</> 
pub fn none() -> Element(a)

A function for rendering nothing. This is mostly useful for conditional rendering, where you might want to render something only if a certain condition is met.

text

</> 
pub fn text(content: String) -> Element(a)

A function for turning a Gleam string into a text node. Gleam doesn’t have union types like some other languages you may be familiar with, like TypeScript. Instead, we need a way to take a String and turn it into an Element somehow: this function is exactly that!

to_string

</> 
pub fn to_string(element: Element(a)) -> String

Convert a Lustre Element to a string. This is not pretty-printed, so there are no newlines or indentation. If you need to pretty-print an element, reach out on the Gleam Discord or open an issue with your use case and we’ll see what we can do!

to_string_builder

</> 
pub fn to_string_builder(element: Element(a)) -> StringBuilder

Convert a Lustre Element to a StringBuilder. This is not pretty-printed, so there are no newlines or indentation. If you need to pretty-print an element, reach out on the Gleam Discord or open an issue with your use case and we’ll see what we can do!

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