Failing in a Javascript Constructor

Question

I'm currently building an (ES6) javascript constructor, and was wondering how I should handle "failure". I was thinking about plainly logging to the console and setting this = undefined;, but for some reason that's an "illegal left-hand side assignment". This is roughly what I had in mind:

class Foo {
  constructor(foo) {
    if (foo === bar) {
      // considered "success"
      this.foo = foo;
    } else {
      // failure
      console.log("oh noes!");
      this = undefined;
    }
  }
}

Would this be considered a wise practice? I'm just trying to understand what the best practice should be, for failing during the use of a constructor.

This is not specific to ES6. This wasn't possible in ES5 either. — Felix Kling
– Felix Kling, Commented Jan 11, 2016 at 18:38

Mike Cluck · Accepted Answer · 2016-01-11 18:05:03Z

1

You can't assign directly to this but if you do want to return undefined in the event of an error, you could use a factory method:

class Foo {
  constructor(foo) {
    if (foo !== bar) {
      throw new Error('oh noes!');
    }
  }
}

let Factory = {
  createFoo(f) {
    try {
      return new Foo(f);
    } catch(e) {
      console.log(e.message);
    }
  }
};

let myFoo = Factory.createFoo(baz);

answered Jan 11, 2016 at 18:05

Mike Cluck

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1 Comment

loganfsmyth Over a year ago

You could also make create a static function on Foo and just do Foo.create(baz) instead.

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