Eager Vue computed property - use for cheap computed properties that always update but that don't trigger updates when their value doesn't change

eager-computed-options-alt.ts

export function useEagerComputed() {
  const properties = []

  function eagerComputed(definitions) {
    const computedProps = {}
    for (const key in definitions) {
      const effect = definitions[key]
      properties.push({ key, effect })
      computedProps[key] = function () {
        return this.$data[key]
      }
    }
    return computedProps
  }

  const mixin = {
    data() {
      const data = {}
      for (const prop of properties) {
        data[prop.key] = undefined
      }
      return data
    },
    created() {
      for (const prop of properties) {
        this.$watch(prop.effect.bind(this), (value) => {
          this.$data[prop.key] = value
        })
      }
    }
  }

  return {
    mixin,
    eagerComputed
  }
}

// Usage in component:

const { mixin, eagerComputed } = useEagerComputed()

export default {
  name: 'HelloWorld',
  mixins: [mixin],
  data() {
    return {
      loadingId: 0,
      id: 0
    }
  },
  methods: {
    update() {
      this.loadingId = (this.loadingId + 1) % 3
    }
  },
  computed: {
    ...eagerComputed({
      isLoading() {
        return this.loadingId === this.id
      }
    }),

    myObj() {
      console.log('computation')
      return {
        isLoading: this.isLoading
      }
    }
  }
}

eager-computed-options.ts

export function eagerComputedMixin<T = any> (key: string, effect: () => T) {
  return {
    data () {
      return {
        [key]: undefined,
      }
    },
    created () {
      this.$watch(effect.bind(this), (value) => {
        this.$data[key] = value
      })
    },
  }
}

eager-computed-vue2.ts

import { watchEffect, readonly } from '@vue/composition-api'

export function eagerComputed<T = any> (effect: () => T) {
  const holder = ref<T>()
  watchEffect(() => {
    holder.value = effect()
  })
  return readonly(holder)
}

eager-computed-vue3.ts

import { watchEffect, readonly } from 'vue'

export function eagerComputed<T = any> (effect: () => T) {
  const holder = ref<T>()
  watchEffect(() => {
    holder.value = effect()
  })
  return readonly(holder)
}

Example with Vue 2: https://codesandbox.io/s/vue-eager-computed-vue2-f7eud?file=/src/components/HelloWorld.vue:147-697