range_via_proxy.js

const handler = {
  get(target, propKey, receiver) {
    if (/^_[0-9]+$/.test(propKey)) {
      const result = [];
      const first = Number(receiver);
      const last = Number(propKey.slice(1));
      for (let i=first; i<=last; i++) {
        result.push(i);
      }
      return result;
    }
    return Reflect.get(target, propKey, receiver);
  }
};
const proxy = new Proxy(Object.prototype, handler);
Object.setPrototypeOf(Number.prototype, proxy);

/*
> 1 . _3
[ 1, 2, 3 ]
> 11 . _14
[ 11, 12, 13, 14 ]
*/

range_via_proxy2.js

const handler = {
  get(target, propKey, receiver) {
    if (/^[0-9]+$/.test(propKey)) {
      const result = [];
      const first = Number(receiver);
      const last = Number(propKey);
      for (let i=first; i<=last; i++) {
        result.push(i);
      }
      return result;
    }
    return Reflect.get(target, propKey, receiver);
  }
};
const proxy = new Proxy(Object.prototype, handler);
Object.setPrototypeOf(Number.prototype, proxy);

/*
> 1[3]
[ 1, 2, 3 ]
> 11[14]
[ 11, 12, 13, 14 ]
*/

You may want something like this in your if statements if you plan on testing this via console.log
if (typeof propKey !== 'symbol' && /^[0-9]+$/.test(propKey)) {

This is amazing btw.