Where to store common component methods in #NUXT.J

Actually i want to know where to store common components methods in #NUXT.JS.

things which i have tried. --> Storing common code in middleware (its use-less) because according to my knowledge middleware is only capable of handling request and response to server.

methods: {

  // states methods.
  SwitchManager: function (__dataContainer, __key, __value) {
    // stand alone debugger for this module.
    let debug = __debug('computed:_3levelSwitch')
    // debug showing function loaded.
    debug('(h1:sizeCheck) creating switch..')
    // switch.
    switch (__key) {
      // fake allow set value to true of given key
      default:
        this[__dataContainer][__key][__value] = true
        break
    }
    return this[__dataContainer][__key][__value]
  },
  SizeCheck: function (__size) {
    // stand alone debugger for this module.
    let debug = __debug('tags:p')
    // debug showing function loaded.
    debug('(p:sizeCheck) checking..')
    // init switch.
    this.SwitchManager('pill', 'size', __size)
  },
  StateCheck: function (__state) {
    // stand alone debugger for this module.
    let debug = __debug('tags:h1')
    // debug showing function loaded.
    debug('(h1:sizeCheck) checking..')
    // init switch.
    this.SwitchManager('pill', 'state', __state)
  }
},
created () {
  // h1 tag size check
  this.SizeCheck(this.size)
  this.StateCheck(this.state)
}

I go for mixins like with plain vue.js. Only difference - for global mixins - I include them as a plugin, but first:

Non global mixins

I would create an extra folder for my mixins. For example in a /mixins/testMixin.js

export default {
  methods: {
    aCommonMethod () {}
  }
}

Then import in a layout, page or component and add it via the mixins object:

<script>
  import commonMixin from '~/mixins/testMixin.js
  export default {
    mixins: [commonMixin]
  }
</script>

Global mixins

For example in a new file plugins/mixinCommonMethods.js:

import Vue from 'vue'

Vue.mixin({
  methods: {
    aCommonMethod () {}
  }
})

Include that file then in nuxt.config.js

plugins: ['~/plugins/mixinCommonMethods']

After that you would have the method everywhere available and call it there with this.commonMethod(). But here an advice from the vue.js docs:

Use global mixins sparsely and carefully, because it affects every single Vue instance created, including third party components. In most cases, you should only use it for custom option handling like demonstrated in the example above. It’s also a good idea to ship them as Plugins to avoid duplicate application.