A template will always need a string as first argument and a list of Bindings to work properly. Consider the following example:

const tmpl = template('<p> </p>', [
  {
    selector: 'p',
    expressions: [
      {
        type: expressionTypes.TEXT,
        childNodeIndex: 0,
        evaluate: (scope) => scope.greeting,
      },
    ],
  },
])

The template object above will bind a simple binding to the <p> tag.

• expressions
  • type: Array<Expression>
  • required: true
  • description: array containing instructions to execute DOM manipulation on the node queried
• type
  • type: Number
  • default:bindingTypes.SIMPLE
  • optional: true
  • description: id of the binding to use on the node queried. This id must be one of the keys available in the bindingTypes object
• selector
  • type: String
  • default: binding root HTMLElement
  • optional: true
  • description: property to query the node element that needs to updated

The bindings supported are only of 4 different types:

• simple to bind simply the expressions to a DOM structure
• each to render DOM lists
• if to handle conditional DOM structures
• tag to mount a coustom tag template to any DOM node

Combining the bindings above we can map any javascript object to a DOM template.

Simple bindings will never modify the DOM tree structure, they will only target a single node.
A simple binding must always contain at least one of the following expression:

• attribute to update the node attributes
• event to set the event handling
• text to update the node content
• value to update the node value

For example, let's consider the following binding:

const pGreetingBinding = {
  selector: 'p',
  expressions: [
    {
      type: expressionTypes.TEXT,
      childNodeIndex: 0,
      evaluate: (scope) => scope.greeting,
    },
  ],
}

template('<article><p> </p></article>', [pGreetingBinding])

In this case we have created a binding to update only the content of a p tag.
Notice that the p tag has an empty text node that will be replaced with the value of the binding expression whenever the template will be mounted

• evaluate
  • type: Function
  • description: function that will receive the current template scope and will return the current expression value
• type
  • type: Number
  • description: id to find the expression we need to apply to the node. This id must be one of the keys available in the expressionTypes object

// update only the class attribute
{ type: expressionTypes.ATTRIBUTE, name: 'class', evaluate(scope) { return scope.attr }}

If the name key will not be defined and the return of the evaluate function will be an object, this expression will set all the pairs key, value as DOM attributes.
Given the current scope { attr: { class: 'hello', 'name': 'world' }}, the following expression will allow to set all the object attributes:

{ type: expressionTypes.ATTRIBUTE, evaluate(scope) { return scope.attr }}

If the return value of the evaluate function will be a Boolean the attribute will be considered a boolean attribute like checked or selected...

// add an event listener
{ type: expressionTypes.EVENT, name: 'onclick', evaluate(scope) { return function() { console.log('Hello There') } }}

To remove an event listener you should only return null via evaluate function:

// remove an event listener
{ type: expressionTypes.EVENT, name: 'onclick', evaluate(scope) { return null } }}

<p><b>Your name is:</b><i>user_icon</i></p>

we could use the following text expression to replace the CommentNode with a TextNode

{ type: expressionTypes.TEXT, childNodeIndex: 2, evaluate(scope) { return 'Gianluca' } }}

each bindings will need a template that will be cloned, mounted and updated for all the instances of the collection.
An each binding should contain the following properties:

• itemName
  • type: String
  • required: true
  • description: name to identify the item object of the current iteration
• indexName
  • type: Number
  • optional: true
  • description: name to identify the current item index
• evaluate
  • type: Function
  • required: true
  • description: function that will return the collection to iterate
• template
  • type: TemplateChunk
  • required: true
  • description: a dom-bindings template that will be used as skeleton for the DOM elements created
• condition
  • type: Function
  • optional: true
  • description: function that can be used to filter the items from the collection

The each bindings have the highest hierarchical priority compared to the other riot bindings. The following binding will loop through the scope.items collection creating several p tags having as TextNode child value dependent loop item received

const eachBinding = {
  type: bindingTypes.EACH,
  itemName: 'val',
  indexName: 'index'
  evaluate: scope => scope.items,
  template: template(' ', [{
    expressions: [
      {
        type: expressionTypes.TEXT,
        childNodeIndex: 0,
        evaluate: scope => `${scope.val} - ${scope.index}`
      }
    ]
  }
}

template('<p></p>', [eachBinding])

if bindings will need a template that will be mounted and unmounted depending on the return value of the evaluate function.
An if binding should contain the following properties:

• evaluate
  • type: Function
  • required: true
  • description: if this function will return truthy values the template will be mounted otherwise unmounted
• template
  • type: TemplateChunk
  • required: true
  • description: a dom-bindings template that will be used as skeleton for the DOM element created

The following binding will render the b tag only if the scope.isVisible property will be truthy. Otherwise the b tag will be removed from the template

const ifBinding = {
  type: bindingTypes.IF,
  evaluate: scope => scope.isVisible,
  selector: 'b'
  template: template(' ', [{
    expressions: [
      {
        type: expressionTypes.TEXT,
        childNodeIndex: 0,
        evaluate: scope => scope.name
      }
    ]
  }])
}

template('<p>Hello there <b></b></p>', [ifBinding])

tag bindings will enhance any child node with a custom component factory function. These bindings are likely riot components that must be mounted as children in a parent component template

A tag binding might contain the following properties:

• getComponent
  • type: Function
  • required: true
  • description: the factory function responsible for the tag creation
• evaluate
  • type: Function
  • required: true
  • description: it will receive the current scope and it must return the component id that will be passed as first argument to the getComponent function
• slots
  • type: Array<Slot>
  • optional: true
  • description: array containing the slots that must be mounted into the child tag
• attributes
  • type: Array<AttributeExpression>
  • optional: true
  • description: array containing the attribute values that should be passed to the child tag

The following tag binding will upgrade the time tag using the human-readable-time template. This is how the human-readable-time template might look like

import moment from 'moment'

export default function HumanReadableTime({ attributes }) {
  const dateTimeAttr = attributes.find(({ name }) => name === 'datetime')

  return template(' ', [
    {
      expressions: [
        {
          type: expressionTypes.TEXT,
          childNodeIndex: 0,
          evaluate(scope) {
            const dateTimeValue = dateTimeAttr.evaluate(scope)
            return moment(new Date(dateTimeValue)).fromNow()
          },
        },
        ...attributes.map((attr) => {
          return {
            ...attr,
            type: expressionTypes.ATTRIBUTE,
          }
        }),
      ],
    },
  ])
}

Here it's how the previous tag might be used in a tag binding

import HumanReadableTime from './human-readable-time'

const tagBinding = {
  type: bindingTypes.TAG,
  evaluate: () => 'human-readable-time',
  getComponent: () => HumanReadableTime,
  selector: 'time',
  attributes: [
    {
      evaluate: (scope) => scope.time,
      name: 'datetime',
    },
  ],
}

template('<p>Your last commit was: <time></time></p>', [tagBinding]).mount(
  app,
  {
    time: '2017-02-14',
  },
)

The tag bindings have always a lower priority compared to the if and each bindings

• evaluate
  • type: Function
  • description: function that will receive the current template scope and will return the current expression value
• type
  • type: Number
  • description: id to find the expression we need to apply to the node. This id must be one of the keys available in the expressionTypes object
• name
  • type: String
  • description: the name to identify the binding html we need to mount in this node

// slots array that will be mounted receiving the scope of the parent template
const slots = [
  {
    id: 'foo',
    bindings: [
      {
        selector: '[expr1]',
        expressions: [
          {
            type: expressionTypes.TEXT,
            childNodeIndex: 0,
            evaluate: (scope) => scope.text,
          },
        ],
      },
    ],
    html: '<p expr1> </p>',
  },
]

const el = template('<article><slot expr0/></article>', [
  {
    type: bindingTypes.SLOT,
    selector: '[expr0]',
    name: 'foo',
  },
]).mount(
  app,
  {
    slots,
  },
  { text: 'hello' },
)

Let's see some cases where we might combine multiple bindings on the same DOM node and how to handle them properly.

Each and If Bindings

Let's consider for example a DOM node that sould handle in parallel the Each and If bindings. In that case we could skip the If Binding and just use the condition function provided by the Each Binding Each bindings will handle conditional rendering internally without the need of extra logic.

Each and Tag Bindings

A custom tag having an Each Binding bound to it should be handled giving the priority to the Eeach Binding. For example:

const components = {
  'my-tag': function ({ slots, attributes }) {
    return {
      mount(el, scope) {
        // do stuff on the mount
      },
      unmount() {
        // do stuff on the unmount
      },
    }
  },
}
const el = template('<ul><li expr0></li></ul>', [
  {
    type: bindingTypes.EACH,
    itemName: 'val',
    selector: '[expr0]',
    evaluate: (scope) => scope.items,
    template: template(null, [
      {
        type: bindingTypes.TAG,
        name: 'my-tag',
        getComponent(name) {
          // name here will be 'my-tag'
          return components[name]
        },
      },
    ]),
  },
]).mount(target, { items: [1, 2] })

The template for the Each Binding above will be created receiving null as first argument because we suppose that the custom tag template was already stored and registered somewhere else.

If and Tag Bindings

Similar to the previous example, If Bindings have always the priority on the Tag Bindings. For example:

const el = template('<ul><li expr0></li></ul>', [
  {
    type: bindingTypes.IF,
    selector: '[expr0]',
    evaluate: (scope) => scope.isVisible,
    template: template(null, [
      {
        type: bindingTypes.TAG,
        evaluate: () => 'my-tag',
        getComponent(name) {
          // name here will be 'my-tag'
          return components[name]
        },
      },
    ]),
  },
]).mount(target, { isVisible: true })

The template for the IF Binding will mount/unmount the Tag Binding on its own DOM node.