try to filter the records from the array of objects

Question

I have the array of objects and i am trying to show the records based upon some filtration,

I am doing in VUE

Here is my code

return this.system.filter(function (item, key) {
        if(key.)
      });

what i am tryin to achieve , if the key is: 1,2,3,4,5 it should be equal to 9 and display A because 9 is equal to A

because my keys are like this

this.system = [
 {
   key:0,"value:"x"
 },
{
   key:1,"value:"x1"
 },
{
   key:2,"value:"x2"
 },
{
   key:3,"value:"x3"
 },
{
   key:4,"value:"x4"
 },
{
   key:5,"value:"x5"
 },
{
   key:6,"value:"x6"
 },
{
   key:7,"value:"x7"
 },
{
   key:8,"value:"x8"
 },
{
   key:9,"value:"A"
 },
{
   key:10,"value:"B"
 },
{
   key:11,"value:"C"
 },
{
   key:12,"value:"D"
 },
]

Answer 1

If I understood you correctly :

new Vue({
  el: '#demo',
  data() {
    return {
      system: [{key:0,value:"x"}, {key:1,value:"x1"}, {key:2,value:"x2" }, {key:3,value:"x3"}, {key:4,value:"x4"}, {key:5,value:"x5"}, {key:6,value:"x6"}, {key:7,value:"x7"}, {key:8,value:"x8"}, {key:9,value:"A"}, {key:10,value:"B"}, {key:11,value:"C"}, {key:12,value:"D"},],
      chose: 0,
    }
  },
  computed: {
    result() {
      return this.system.filter(item => {
        if (+this.chose > 0 && +this.chose < 6 || +this.chose === 9) {
          return item.key === 9
        } else {
          return item.key === +this.chose
        }
      })
    }
  }
})

<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.17/vue.js"></script>
<div id="demo">
  <input v-model="chose" type="number" />
  {{ result }}
</div>

Answer 2

As per my understanding, You want to return value of value property based on the value of key property. If Yes, You can simply achieve that by using Array.find() method. Here you go :

const system = [
  {
    key:0,value:"x"
  },
  {
    key:1,value:"x1"
  },
  {
    key:2,value:"x2"
  },
  {
    key:3,value:"x3"
  },
  {
    key:4,value:"x4"
  },
  {
    key:5,value:"x5"
  },
  {
    key:6,value:"x6"
  },
  {
    key:7,value:"x7"
  },
  {
    key:8,value:"x8"
  },
  {
    key:9,value:"A"
  },
  {
    key:10,value:"B"
  },
  {
    key:11,value:"C"
  },
  {
    key:12,value:"D"
  }
];

const res = system.find(({key}) => key === 9);

console.log(res.value);