Vue.js 2 Component Props

Props are used to pass down state to child components. Learn all about them

• Define a prop inside the component
• Accept multiple props
• Set the prop type
• Set a prop to be mandatory
• Set the default value of a prop
• Passing props to the component

Define a prop inside the component

Props are the way components can accept data from components that include them (parent components).

When a component expects one or more prop, it must define them in its props property:

Vue.component('user-name', {
  props: ['name'],
  template: '<p>Hi {{ name }}</p>'
})

or, in a Vue Single File Component:

<template>
  <p>{{ name }}</p>
</template>

<script>
export default {
  props: ['name']
}
</script>

Accept multiple props

You can have multiple props by appending them to the array:

Vue.component('user-name', {
  props: ['firstName', 'lastName'],
  template: '<p>Hi {{ firstName }} {{ lastName }}</p>'
})

Set the prop type

You can specify the type of a prop by using an object instead of an array, using the name of the property as the key of each property, and the type as the value:

Vue.component('user-name', {
  props: {
    firstName: String,
    lastName: String
  },
  template: '<p>Hi {{ firstName }} {{ lastName }}</p>'
})

The valid types you can use are:

• String
• Number
• Boolean
• Array
• Object
• Date
• Function
• Symbol

When a type mismatches, Vue alerts (in development mode) in the console with a warning.

Prop types can be more articulated.

You can allow multiple different value types:

props: {
  firstName: [String, Number]
}

Set a prop to be mandatory

You can require a prop to be mandatory:

props: {
  firstName: {
    type: String,
    required: true
  }
}

Set the default value of a prop

You can specify a default value:

props: {
  firstName: {
    type: String,
    default: 'Unknown person'
  }
}

For objects:

props: {
  name: {
    type: Object,
    default: {
      firstName: 'Unknown',
      lastName: ''
    }
  }
}

default can also be a function that returns an appropriate value, rather than being the actual value.

You can even build a custom validator, which is cool for complex data:

props: {
  name: {
    validator: name => {
      return name === 'Flavio' //only allow "Flavios"
    }
  }
}

Passing props to the component

You pass a prop to a component using the syntax

<ComponentName color="white" />

if what you pass is a static value.

If it’s a data property, you use

<template>
  <ComponentName :color=color />
</template>

<script>
...
export default {
  //...
  data: function() {
    return {
      color: 'white'
    }
  },
  //...
}
</script>

You can use a ternary operator inside the prop value to check a truthy condition and pass a value that depends on it:

<template>
  <ComponentName :colored="color == 'white' ? true : false" />
</template>

<script>
...
export default {
  //...
  data: function() {
    return {
      color: 'white'
    }
  },
  //...
}
</script>