adjust console.log behaviour of custom object

The previous answer has been deprecated in newer versions of node. The method one needs to implement now is the symbol [util.inspect.custom].

For example:

const util = require('util');

class Custom {
  constructor(foo, bar) {
    this.foo = foo;
    this.bar = bar;
  }

  [util.inspect.custom](depth, opts) {
    return this.foo + this.bar;
  }
}

console.log(new Custom(3, 5)); // Prints '8'