Custom printing from console.log?

Question

Let\'s say I have this class.

class Attribute {
  constructor(name) {
    this.name = name;
  }
}

And I create an instance and log it to the c

Answer 1

A sane solution would probably be to use a custom logging function that stringifies Attribute values.

However, if you have a vendetta against people who need to maintain your code in the future, one solution that meets the technical requirements of this question is to have your class extend a type that console.log automatically serializes to string, like RegExp. When you console.log a RegExp instance, Chrome (and probably other environments) automatically serializes it to its bare /.../ expression. Simply overwrite what string it should serialize to by supplying a custom toString function, and you've got exactly what you asked for.

class Attribute extends RegExp {
  constructor(name) {
    super();
    this.name = name;
  }
  toString() {
    return this.name
  }
}
var test = new Attribute('Large');
console.log(test);

This is roughly equivalent to answering the question "How do I stop my house from flooding?" with "Put your house on a giant raft" instead of "Put some caulk in your basement" or "Move somewhere else." Some side effects will include:

• Your objects will inherit regular expression properties like global and exec

• Testing if your object is instanceof RegExp will of course return true, which might cause your object to be valid inputs for routines that only expect to operate on regular expression objects

Using further dark magic, you can solve the these issues by doing

Object.setPrototypeOf(Attribute.prototype, Object.prototype);

immediately after your class definition, which will ensure that your this object will simply be run through the RexExp constructor (thereby flagging it for stringified log output) but not inherit from RexExp.prototype. By mixing class and prototype syntax together, you also ensure that your code is confusing and everyone is actively afraid of it.

Answer 2

apsiller's answer works great in Chrome and Firefox, but unfortunately, it doesn't work in Node. However, after some experimentation and research, I found a solution that does work in Node.

It turns out that Node's implementation of console.log has a built-in customization point, util.inspect.custom, so all you have to do is define a method with that symbol that returns whatever you want to print.

class Attribute {
  constructor(name) {
    this.name = name;
  }
  [require('util').inspect.custom](){
    return `{Attribute} ${this.name}`;
  }
}

Answer 3

class Attribute {
  constructor(name) {
    this.name = name;
  }
  toString(){//simply set the to String method?
    return "{Attribute} "+this.name;
  }
}

As console.log does not call to String you either do:

const test = new Attribute('Large');
console.log(test+"");

or you create your own logging function