I've searched the site for this question and got the following answer:

function instance_of(V, F) {
  var O = F.prototype;
  V = V.__proto__;
  while (true) {
    if (V === null)
      return false;
    if (O === V)
      return true;
    V = V.__proto__;
  }
}

It's from https://stackoverflow.com/a/9220317/12974414.

But I tested the following code, found something weird:

console.log( (10).__proto__ === Number.prototype ) // true
console.log( instance_of(10, Number ) )            // true
console.log( 10 instanceof Number )                // false

function instance_of(V, F) {
  var O = F.prototype;
  V = V.__proto__;
  while (true) {
    if (V === null)
      return false;
    if (O === V)
      return true;
    V = V.__proto__;
  }
}

How to explain this and how does instanceof operator actually work in JS ?