Fela plugin for Vue
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readme.md

Fela plugin for Vue

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Installation

yarn add vue-fela

Usage

import Vue from 'vue'
import VueFela from 'vue-fela'
import { createRenderer } from 'fela'

// 1. Create a Fela renderer
const renderer = createRenderer()

// 2. Install the plugin and pass the renderer as an option
Vue.use(VueFela, { renderer })

When the plugin is installed, a $fela property is set on Vue's prototype making it available on each component instance. The $fela property provides a reference to the Fela Renderer instance that was passed as an option when the plugin was installed.

The Fela Renderer instance is also provided through the inject interface on a fela key. This allows you to access the renderer within functional Vue components.

Check out a full working example using Nuxt.

Rendering Rules

Since a Fela Renderer instance is assigned to Vue's prototype, you can reference and use within a Vue component via this.$fela.

See the Single File Component example below:

<template>
  <div :class="className"/>
</template>

<script>
const rule = (props) => ({
  color: props.color,
  margin: 10
})

export default {
  props: {
    color: {
      type: String,
      default: 'red'
    }
  },
  computed: {
    className() {
      return this.$fela.renderRule(rule, this)
    }
  }
}
</script>

In the example above, we are passing this as the rule's props to Fela's renderRule function. Doing so will give the rule access to all the component instance properties such as color to derive the styles.

You can of course pass any arbitrary props object as the second argument to renderRule.

mapRule(rule, optProps)

To save having to define a computed prop function and return this.$fela.renderRule(rule, props) each time, a mapRule helper is provided:

<template>
  <div :class="className"/>
</template>

<script>
import { mapRule } from 'vue-fela'

const rule = (props) => ({
  color: props.color,
  margin: 10
})

export default {
  props: {
    color: {
      type: String,
      default: 'red'
    }
  },
  computed: {
    className: mapRule(rule)
  }
}
</script>

Passing optProps as the second argument to mapRule is optional.

If optProps is omitted (like in the example above) then the Vue component instance will be passed by default. Typically this is the desired behaviour since a component's styles will generally want to be the result of its state.

In the example above, the color prop can be configured by a parent component. This value will then be available within the component instance via this.color. If color is not set by the parent component, it will default to 'red' since we have set the default field in the props color definition.

As you might expect, all properties and methods on a Vue component instance can be used within a rule:

  • props values set by parent components
  • data values set when the component is initialised
  • computed values derived from other properties and state
  • methods that return values

Since the class names being returned from mapRule are assigned to the component's computed props object, any change in state referenced by a rule will trigger an update and return new class names.

mapRules(rules, optMap, optProps)

Taking it one step further, the mapRules helper repeats the work of mapRule—but expects an object map of rules rather than a single rule function:

<template>
  <div :class="container">
    <h1 :class="heading">Kitten Socks</h1>
    <p :class="body">The purrrfect gift for your cat.</p>
  </div>
</template>

<script>
import { mapRules } from 'vue-fela'

const rules = {
  // We can use object destructuring on the rule props
  container: ({ highlight, textAlign }) => ({
    backgroundColor: highlight ? '#DDF' : '#DDD',
    padding: 16,
    textAlign
  }),
  heading: ({ highlight }) => ({
    fontWeight: highlight ? 700 : 400,
    fontSize: 24
  }),
  body: ({ highlight }) => ({
    color: highlight ? '#F00' : '#888',
    fontSize: 16
  })
}

export default {
  props: {
    highlight: {
      type: Boolean,
      default: false
    },
    textAlign: {
      type: String,
      default: 'left'
    }
  },
  computed: mapRules(rules)
}
</script>

Writing all your rules in a component can start to get a little cumbersome, so you might want to consider breaking them out into a separate file:

// component-rules.js
export default {
  container: ({ highlight, textAlign }) => ({
    backgroundColor: highlight ? '#DDF' : '#DDD',
    padding: 16,
    textAlign
  }),
  heading: ({ highlight }) => ({
    fontWeight: highlight ? 700 : 400,
    fontSize: 24
  }),
  body: ({ highlight }) => ({
    color: highlight ? '#08F' : '#888',
    fontSize: 16
  })
}

...and then import them into your Vue component:

<template>
  <div :class="container">
    <h1 :class="heading">Kitten Socks</h1>
    <p :class="body">The purrrfect gift for your cat.</p>
  </div>
</template>

<script>
import { mapRules } from 'vue-fela'
import rules from './component-rules'

export default {
  props: {
    highlight: {
      type: Boolean
    },
    textAlign: {
      type: String,
      default: 'left'
    }
  },
  computed: mapRules(rules)
}
</script>

Calling mapRules(rules, optMap, optProps) with no optMap argument will result in all rules being returned and assigned to the component's computed props.

In the example above, this would assign container, heading and body to the component's computed props. These 3 props can then be used as class names on the 3 respective elements in the template.

This behaviour might not always be desirable, so mapRules provides another level of control with the optMap argument.

If you have used Vuex's mapping helpers the following interface should look familiar to you.

optMap

The optMap argument can either be:

  1. An Array of Strings where:
    • String values are the names of the rules to include in the object that is returned
    • This allows you to filter out only the rules you require
    • It does not allow you to rename the rules
  2. An Object of key values where:
    • Keys are aliases to use as the computed prop names in the object that is returned
    • Values are the names of the rules in the object map
    • This allows you to both filter and rename rules

For example, using the same component and rules map from the example above:

<template>
  <div :class="container">
    <h1 :class="title">Kitten Socks</h1>
    <p>The purrrfect gift for your cat.</p>
  </div>
</template>

<script>
import { mapRules } from 'vue-fela'
import rules from './component-rules'

export default {
  props: {
    highlight: {
      type: Boolean
    },
    textAlign: {
      type: String,
      default: 'left'
    }
  },
  computed: {
    ...mapRules(rules, [
      'container' // Only return the container rule
    ]),
    ...mapRules(rules, {
      title: 'heading' // Only return the heading rule, but rename it to 'title'
    })
  }
}
</script>

In the example above you can see that we have used the object spread operator to merge multiple calls to mapRules onto the component's computed props object. We have also omitted the body rule from the component-rules.js map.

optProps

Finally, much like the mapRule helper, optProps can be passed as the third argument to mapRules. Omitting optProps will result in the component instance being passed to each of the rules as the props argument by default.

mapStyles(rules, optMap, optProps)

If your component has properties that clash with your rule names when mapping them to the computed object—you have a couple of options:

  1. Pass an optMap argument to mapRules to alias your rule names to different ones eg. iconClass: 'icon'
  2. Use a naming convention for all your rules that separates them from your component props eg. iconRule or iconClass

The first option requires more code in your components. The second option compromises the precise naming of your rules. Neither options are ideal.

As a third option you can use the mapStyles helper.

This helper works in exactly the same way as mapRules, but rather than returning an object map of computed prop functions, it returns a single computed function.

The computed function returned from the mapStyles helper will then return an object map of class names that are the result of rendering your rules.

This allows you to assign all your rules to a single computed property eg. styles and render the result of each rule within your template using dot syntax eg. styles.icon:

<template>
  <div>
    <svg :class="styles.icon">...</svg>
    <span :class="styles.text">{icon}</span>
  </div>
</template>

<script>
import { mapStyles } from 'vue-fela'

const rules = {
  // Here we have a rule name that is the
  // same as one of the component props
  icon: ({ size, color }) => ({
    width: size,
    height: size,
    fill: color
  }),
  text: ({ size, color }) => ({
    fontSize: size,
    color
  })
}

export default {
  props: {
    icon: {
      type: String
    },
    size: {
      type: Number,
      default: 16
    },
    color: {
      type: 'String',
      default: 'red'
    }
  },
  computed: {
    // All rules are assigned to a single computed 'styles'
    // property and do not clash with any other props
    styles: mapStyles(rules)
  }
}
</script>

The function signature of mapStyles(rules, optMap, optProps) is identical to mapRules(rules, optMap, optProps).

Read the documentation on optMap and optProps above.

renderRule(renderer, rule, props)

When creating functional Vue components you can inject the Fela Renderer instance via the fela key:

export default {
  functional: true,
  inject: [ 'fela' ],
  render(h, { data, children, injections }) {
    // Reference to Fela Renderer instance
    const renderer = injections.fela
    return h('span', data, children)
  }
}

To render a single Fela rule you can either use the Fela Renderer instance's renderRule method directly or you can use the renderRule helper provided by Vue Fela. They do exactly the same thing—this is just a matter of style:

import { renderRule } from 'vue-fela'

const rule = ({ size }) => ({ width: size, height: size })

export default {
  functional: true,
  inject: [ 'fela' ],
  props: { size: Number },
  render(h, { props, children, injections }) {
    const renderer = injections.fela
    // The following 2 lines return exactly the same value
    const class1 = renderRule(renderer, rule, props)
    const class2 = renderer.renderRule(rule, props)
    // class1 === class2
    return h('span', {
      class: [ class1, class2 ] // a b
    }, children)
  }
}

renderRules(renderer, rules, props, optMap)

When using an object map of rules within a functional Vue component you can use the renderRules helper provided by Vue Fela:

import { renderRules } from 'vue-fela'

const rules = {
  container: ({ fillColor }) => ({
    backgroundColor: fillColor,
    padding: '8px'
  }),
  text: ({ textColor }) => ({
    color: textColor,
    fontSize: '16px'
  }),
}

export default {
  functional: true,
  inject: [ 'fela' ],
  props: {
    fillColor: String,
    textColor: String
  },
  render(h, { props, children, injections }) {
    const renderer = injections.fela
    const styles = renderRules(renderer, rules, props)
    return h('div', {
      class: styles.container
    }, [
      h('span', {
        class: styles.text
      }, children)
    ])
  }
}

You can also optionally pass optMap as the final argument to the renderRules helper.

This works in exactly the same way as documented above in the mapRules helper.

Rendering Styles

To render the styles cached by the Fela Renderer we need to use fela-dom.

However, since Fela works on both the client and the server, the method for rendering the cached styles differs between environments.

To simplify this, VueFela handles the logic of determining what to do in each environment automatically.

Plugin Options

You can disable automatic rendering via the plugin options when installing VueFela:

import Vue from 'vue'
import VueFela from 'vue-fela'
import { createRenderer } from 'fela'
import { render } from 'fela-dom'

const renderer = createRenderer()

Vue.use(VueFela, {
  renderer, // required
  autoRender: false
})

// Manually render the styles (client-side)
render(renderer)

Options that can be configured when the plugin is installed are as follows:

Option Type Default Description
renderer Object Fela Renderer instance. Required
autoRender Boolean true Enable/disable automatic rendering. When set to false the ssr and metaKeyName properties are ignored
ssr Boolean true Enable/disable SSR
metaKeyName String head Vue Meta keyName option
This is configured to work with Nuxt by default

An example using Vue Meta's default values while disabling SSR can be seen below:

import Vue from 'vue'
import VueFela from 'vue-fela'
import { createRenderer } from 'fela'

Vue.use(VueFela, {
  renderer: createRenderer(), // required
  metaKeyName: 'metaInfo',
  ssr: false
})

Universal Rendering

The easiest way to create universal Vue applications is with Nuxt. Nuxt takes care of setting up the logic for rendering Vue components on the server and rehydrating them on the client.

Nuxt uses vue-meta to render and update tags in the <head> of your pages. Vue Meta provides the mechanism Vue Fela needs for rendering the cached styles on the server and sending them to the client.

Because of this, the vue-fela plugin is configured to work with vue-meta using Nuxt's configuration options by default.

Nuxt Example

To setup Vue Fela with Nuxt you will need to create a file in the plugins directory:

// plugins/fela.js
import Vue from 'vue'
import VueFela from 'vue-fela'
import { createRenderer } from 'fela'

// 1. Create a Fela renderer
const renderer = createRenderer()

// 2. Install the plugin and pass the renderer as an option
Vue.use(VueFela, { renderer })

Then add the plugin to Nuxt's configuration:

// nuxt.config.js
module.exports = {
  plugins: [
    'plugins/fela'
  ]
}

Check out a full working example using Nuxt.

Tests

Tests are written using jest and vue-test-utils.

To run the tests after cloning the repository and installing its dependencies:

yarn test

To run the tests in watch mode:

yarn test-watch

To generate a coverage report:

yarn test-coverage

Author

Matthew Wagerfield

License

MIT