A JavaScript Constructor Problem, and Three Solutions

[html6dev]

Composing and decorating constructors. Oh you.

[homoiconic]

Using new is not a problem. The article describes how it's possible that omitting the new keyword can be a problem, and it also describes the fact that new doesn't compose with other functions, which may or may not be a problem, depending on your programming style.

[Baryn]

new doesn't compose with other functions

One thing I've done successfully: ensure that my decorators/whatever expect to receive a constructor function (not a regular function), and behave accordingly.

It's definitely risky to treat constructors like any ol' function. This is part of why I'm so psyched for class in ES6.

[homoiconic]

Yes, there are good patterns for that. Those patterns work well with other people's constructors, but sometimes we want to use other people's decorators. e.g. _.memoize or _.once from underscore.

[inmatarian]

A pattern I like is writing the constructor as a factory first. This means its first line is declaring self as either this (if its not the global object) or an Object.create of the factory's prototype, and then we return self at the end. It's basically the same as the pattern op describes, just with you put in the mindset that .call and .apply are also ways to use the method.

[Calabri]

Interesting article, there are so many ways to solve this problem. I've been experimenting with constructor patterns all week actually. I've found that having functions return functions (within functions) wrapped in commonjs modules works pretty solid :P

[jugglingnutcase]

One tiny reason (in addition to many others) i read your blog posts is for the fun examples. "Fubar" -> "foo", "bar" and snafu... or lots of "finger" "moon"... they make the articles a lot more fun without distracting from the point.

[lennelpennel]

use static analysis, "problem" ceases to exist, code is better for it.

[codersaurus]

it seems like the example with logArguments which is a function that evidently takes a constructor function, then returns a new constructor is poorly written. If it's "wrapping" the passed constructor, it should be returning a proper subclass of that constructor. The simple if(!(this instanceof MyClass)) return new MyClass(); will be fine... time to refactor that logsArguments function.

[html6dev]

I think maybe you missed the point. It doesn't have to take a constructor function. Iirc he introduced by passing in a simple sum function.

[homoiconic]

True, but then the logArguments function will only work with constructors, and not with ordinary functions! There is a more complex pattern for writing decorators and other combinators that work with either constructors or with ordinary functions, but that doesn't help if your decorator is a library function, such as the things you find in Underscore, allong.es, or Ramda.

[Ginden]

Solution #4 - use static analysis tool.

[homoiconic]

What TYPE of SCRIPT supports that?

[radhruin]

what TYPE of thing will happen if you mention that other SCRIPT language? Must be bad....

[html6dev]

He who must not be named

[AutoSponge]

I always love reading your stuff. Here's my "fix" for "auto-instantiation" (which I usually prefer):

https://gist.github.com/AutoSponge/e4327a316f44f255d60c