Vue.js Filters: Formatting and Transforming Data in Templates

Vue.js filters provide a convenient way to format and transform dynamic data used in a template. Filters do not modify component data but only affect the output of the template.

For example, consider a scenario where we want to print a name:

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

<script>
export default {
  data() {
    return {
      name: 'Flavio'
    }
  }
}
</script>

But what if we want to check if name has a value and print “there” if it doesn’t? Filters come to the rescue:

<template>
  <p>Hi {{ name | fallback }}!</p>
</template>

<script>
export default {
  data() {
    return {
      name: 'Flavio'
    }
  },
  filters: {
    fallback: function (name) {
      return name ? name : 'there'
    }
  }
}
</script>

In the above example, the fallback filter is applied using the syntax {{ name | fallback }}. Filters can be chained as well, allowing us to apply multiple filters one after another:

{{ name | fallback | capitalize }}

Beyond basic usage, filters can also accept parameters:

<template>
  <p>Hello {{ name | prepend('Dr.') }}</p>
</template>

<script>
export default {
  data() {
    return {
      name: 'House'
    }
  },
  filters: {
    prepend: (name, prefix) => {
      return `${prefix} ${name}`
    }
  }
}
</script>

In the above example, the prepend filter accepts a prefix parameter, which allows us to add a prefix to the name.

For more advanced filtering capabilities, you can explore the vue2-filters package from npm. It offers a wide range of pre-made filters, including options like capitalize, uppercase, lowercase, placeholder, truncate, currency, pluralize, and more.