Create a class with add, remove, random - technical interview example question https://jsfiddle.net/1jhfvpz5/1/

store.js

class Store {
  values = [];
  indices = {};

  constructor() {
    this.values = [];
    this.indices = {};
  }
  
  add(value) {
    let index;
   
    if (typeof(value) === 'object') {
    	this.addRange(value);
    }
    else {
      if (!this.indices[value]) {
        this.values.push(value);
        index = this.values.length - 1;
        this.indices[value] = index;
      }
    }
    
    return index;
  }

  addRange(values) {
    values.forEach(value => {
       this.add(value);
    });
  }
 
  remove(value) {
    const index = this.indices[value];
    if (index !== undefined) {
    	const swapValue = this.values.pop();
        this.values[index] = swapValue;
        this.indices[swapValue] = index;
        delete this.indices[value];
    }
    
    return index;
  }
  
  random() {
    const index = Math.floor(Math.random() * this.values.length);
    return this.values[index];
  }
  
  toString() {
    return this.values.toString();
  }
}

zclient.js

const store = new Store();
store.add(1);
store.add([2, 3, 4, 5, 6, 7, 8, 9])
console.log(store.toString());
store.remove(5);
console.log(store.toString());

let counts = {};
const total = 10000;
for (let i=0; i<total; i++) {
  const value = store.random();
  counts[value] = counts[value] ? counts[value] + 1 : 1;
}
Object.keys(counts).forEach(value => {
  const count = counts[value];
  console.log(`${value}: ${count / total * 100}`);
});

store.remove(1);
store.remove(3);
store.remove(8);
console.log(store.toString());

counts = {};
for (let i=0; i<total; i++) {
  const value = store.random();
  counts[value] = counts[value] ? counts[value] + 1 : 1;
}
Object.keys(counts).forEach(value => {
  const count = counts[value];
  console.log(`${value}: ${count / total * 100}`);
});

zoutput.txt

1,2,3,4,5,6,7,8,9
1,2,3,4,9,6,7,8

1: 12.45
2: 12.46
3: 12.17
4: 12.839999999999998
6: 12.32
7: 12.8
8: 12.55
9: 12.41

6,2,7,4,9

2: 19.59
4: 20.01
6: 19.85
7: 20.169999999999998
9: 20.380000000000003