Ember.js ArrayProxy set() Method

import Route from "@ember/routing/route";

export default class StudentsRoute extends Route {
    partyItems = [
        'Digital Camera',
        'Jugs, cups & straws',
        'Balloons',
        'Scissors',
        'Cold Drink',
        'Table Confetti',
        'Party Hats',
        'Wine',
        'Napkins',
        'Party Plates',
        'Speakers',
        'Music System',
        'Cups',
    ];
    len;
    model() {
        return this.partyItems;
    }
    setupController(controller, model) {
        super.setupController(controller, model);
        controller.set("partyItems", this.partyItems);
        controller.set("len", this.len);
        controller.set("item", this.item);
    }
}

import Ember from "ember";

export default Ember.Controller.extend({
    actions: {
        show_first() {
            let ans = this.partyItems.get('firstObject');
            alert(ans)
        },
        show_last() {
            let ans = this.partyItems.get('lastObject');
            alert(ans)
        },
        show_len() {
            let S_len = this.partyItems.length;
            this.set('len', S_len)
            alert('Length of List is ' + this.len);
        },
        check_items(data) {
            let temp = this.partyItems.without(data)
            alert(temp.join('\n'))
        },
        show() {
            let temp = this.partyItems.get('[]');
            alert(temp.join('\n'))
        },

    },
});

{{page-title "set"}}
<h3>List of Items: </h3>
<table>
    <ul>
        {{#each @model as |student|}}
              <li>{{student}}</li>
        {{/each}}
    </ul>
</table>
<br /><br />
<div>
    <label>Enter Item: </label>
      {{input value=this.temp}}
</div>
<input
    type="button"
      id="check-atIndex"
      value="Print Except this Item"
      {{action "check_items" this.temp}}
/>
<br /><br />
<input
    type="button"
      id="show-item"
      value="Pop up All Items"
      {{action "show"}}
/>
<br /><br />
<input
    type="button"
      id="first-item"
      value="Show First Item"
      {{action "show_first"}}
/>
<br /><br />
<input
    type="button"
      id="show-item2"
      value="Show Last Item"
      {{action "show_last"}}
/>
<br /><br />
<input
    type="button"
      id="print-list"
      value="Print length of List"
      {{action "show_len"}}
/>
{{outlet}}

import Route from '@ember/routing/route';

export default class PartyRoute extends Route {
    partyItems = [
        'Oxygen',
        'Source Code',
        'Infine',
        'Tenet',
        'SpiderHead',
        'The Thing',
        'A Quiet Place',
        'The Invisible Man',
        'Looper',
        'Ad Astra'
    ];
    item;
    idx;
    len;
    model() {
        return this.partyItems;
    }
    setupController(controller, model) {
        super.setupController(controller, model);
        controller.set('partyItems', this.partyItems);
        controller.set('item', this.item);
        controller.set('idx', this.idx);
        controller.set('len', this.len);
    }
}

import Ember from 'ember';
import { } from '@ember/array';

export default Ember.Controller.extend({
    actions: {
        remove_Item(item) {
            this.partyItems.set('[]', this.partyItems.without(item));
        },
        print_len() {
            alert(this.partyItems.length)

        },
        print_first() {
            let ans = this.partyItems.get('firstObject');
            alert(ans)
        },
        print_last() {
            let ans = this.partyItems.get('lastObject');
            alert(ans)
        },
    },
});

{{page-title "set"}}
<h3>Here is a list of items: </h3>
<ul>
    {{#each @model as |party|}}
        <li>{{party}}</li>
      {{/each}}
</ul>
<br />
<div>
    <label>Enter value: </label>
      {{input value=this.item}}
</div>
<div>
    <input
        type="button"
        id="search-item"
        value="Remove this item"
        {{action "remove_Item" this.item}}
      />
</div>
<br />
<div>
    <input
        type="button"
        id="len-list"
        value="Print Total length of list"
        {{action "print_len"}}
      />
</div>
<br />
<div>
    <input
        type="button"
        id="list-first"
        value="Print first element of list"
        {{action "print_first"}}
      />
</div>
<br />
<div>
    <input
        type="button"
        id="list-last"
        value="Print last element of list"
        {{action "print_last"}}
      />
</div>
{{outlet}}