Vue: applying css class if specific condition is met

I’m making a custom image slider using vuex, I want to apply a specific class to the dots used for navigating the sliders, so if the dot is active it will be applied a dotActive class. I want to use activeSlider variable for this

This is the slider component:

<template>
<section class="slider_maincontainer">
    <transition-group name="slider-fade">
        <div class="slider_item" v-show="activeSlider===1" style="background-color:red;">
            <!--slider content-->
        </div>
        <div class="slider_item" v-show="activeSlider===2" style="background-color:blue;">
            <!--slider varied content-->
        </div>
        <div class="slider_item" v-show="activeSlider===3" style="background-color:green;">
            <!--another slider-->
        </div>
    </transition-group>
    <button class="slider_buttom_prev" @click="prevSlider()">
        <i class="slider_buttom_icon fas fa-angle-left"></i>
    </button>
    <button class="slider_buttom_next" @click="nextSlider()">
        <i class="slider_buttom_icon fas fa-angle-right"></i>
    </button>
    <div class="slider_dots_container">
    <!--how to apply custom class to this dot depending of activeIndex
        <span class="slider_dots_dot" v-for="slider in slidersCount" :key="slider" @click="goToSlider(slider)"></span>
    </div>
</section>
</template>
<!--SCRIPTS-->
<script>
import { mapState, mapActions } from 'vuex'
export default {
name: 'MainSlider',

computed:{
    ...mapState('MainSlider', ['activeSlider', 'slidersCount']),
},

mounted() {
    console.log(this.$options.name+' component successfully mounted');
    this.startSlider();
},

methods:{
    ...mapActions('MainSlider', ['nextSlider', 'prevSlider']),
}
};
</script>

And my Slider Store:

//STATE
const state = {
  slidersCount: 3,
  sliderInterval: 3000,
  activeSlider: 1,

}

//GETTERS
const getters = {

}

//ACTIONS
const actions = {


    prevSlider ({ commit, state }) {
        if(state.activeSlider == 1){
            commit( 'TO_LAST_SLIDER' );
        }
        else{
            commit( 'PREV_SLIDER' );
        }
    },


    nextSlider ({ commit, state }) {
        if(state.activeSlider == state.slidersCount){
            commit( 'TO_FIRST_SLIDER' );
        }
        else{
            commit( 'NEXT_SLIDER' );
        }
    },


    goToSlider ({ commit, sliderIndex }) {
        commit('GO_TO_SLIDER', sliderIndex)
        
    },



}

//MUTATIONS
const mutations = {


    PREV_SLIDER (state) {
        state.activeSlider--;
    },

    NEXT_SLIDER (state) {
        state.activeSlider++;
    },

    GO_TO_SLIDER (state, sliderIndex) {
        state.activeSlider = sliderIndex;
    },

    TO_FIRST_SLIDER (state) {
        state.activeSlider = 1;
    },

    TO_LAST_SLIDER (state) {
        state.activeSlider = state.slidersCount;
    },


}

export default {
    namespaced: true, state, getters, actions, mutations
  }

I know this could be made easier if each dom slider where associated with an object along with using a v-for but afaik I can’t do that with raw dom element, I’m not getting the slider images from backend or anything.

Answer

You could use a class binding that activates the dotActive class for a specific span only when activeSlider matches the span‘s slider index:

<span v-for="slider in sliderCount"
      :class="{ dotActive: slider === activeSlider }">

new Vue({
  el: '#app',
  data: () => ({
    activeSlider: 1,
    sliderCount: 3,
  }),
  methods: {
    slide(diff) {
      let slider = (this.activeSlider + diff) % (this.sliderCount + 1);

      // wrap around
      if (slider === 0) {
        slider = (diff > 0)
          ? 1
          : this.sliderCount;
      }

      this.activeSlider = slider;
    },
  }
})

#app {
  display: flex;
  justify-content: center;
  flex-direction: column;
  align-items: center;
}
.button_container {
  margin: 20px; 
}
.slider_dots_container {
  width: 5%;
  display: flex;
  justify-content: space-around;
}
.slider_dots_dot {
  border: solid 2px lightgray;
  border-radius: 50%;
  height: 1px;
}
.dotActive {
  border-color: black;
}

<script src="https://unpkg.com/vue@2.5.17"></script>

<div id="app">
  <div class="button_container">
    <button @click="slide(-1)">Prev</button>
    <button @click="slide(1)">Next</button>
    {{activeSlider}}
  </div>
  <div class="slider_dots_container">
    <span v-for="slider in sliderCount"
          :key="slider"
          class="slider_dots_dot"
          :class="{ dotActive: slider === activeSlider }">
    </span>
  </div>
</div>