Conflict between `no-new` and `no-unused-vars` rules

[synthecypher]

If I want to instantiate a class as part of an initialization process but I do nothing with the instance after the fact I run into the two dilemmas.

// no-unused-vars
const gameEngineInstance = new GameEngine()

If I remove the unused variable I get the following

// no-new
new GameEngine()

If I do the following it won't instantiate the class.

GameEngine()

So what should I do in this example to comply with standard?

[yoshuawuyts]

Change your API so new isn't used for side effects, or disable the rule for that specific line. Warnings exist to tell you something is a bad idea. Disabling rules is possible so you can disagree.

…

On Tue, Jul 25, 2017, 18:54 Joshua Barnett ***@***.***> wrote: If I want to instantiate a class as part of an initialization process but I do nothing with the instance after the fact I run into the two dilemmas. // no-unused-varsconst gameEngineInstance = new GameEngine() If I remove the unused variable I get the following // no-newnew GameEngine() If I do the following it won't instantiate the class. GameEngine() So what should I do in this example to comply with standard? — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#958>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ACWlep8YoV476xyZQZcNzFCTp23jPl_Fks5sRh3hgaJpZM4Oi1Ha> .

[LinusU]

I agree with what @yoshuawuyts said, it's very bad practice to have side effects happen in a constructor. I would recommend refactoring so that it isn't necessary.

If you do want to continue doing so, you can disable linting for that line, like so:

// eslint-disable-next-line
new GameEngine()

[synthecypher]

@LinusU can you link me to some information or an example of how I might write such an API?

[bcomnes]

Move the side-effects into a function or method call of an instance.

E.G. collect options on instantiation, then once instantiated, run a .mount() or .start() method that does whatever side-effects you were doing in the instantiation.

[LinusU]

In this specific case, I can imagine that the GameEngine sets up some kind of loop that runs every frame or similar. Instead of doing that in the constructor move that to a .start() function.

e.g.

old:

class GameEngine {
  constructor () {
    // ...

    setInterval(() => this.renderFrame(), 1000 / 30)
  }

  // ...
}

// ...

new GameEngine()

new:

class GameEngine {
  constructor () {
    // ...
  }

  start () {
    setInterval(() => this.renderFrame(), 1000 / 30)
  }

  // ...
}

// ...

const engine = new GameEngine()

engine.start()

[synthecypher]

I'm The constructor it initialises variables with sensible defaults does that count as a side effect?

…

On Mon, 31 Jul 2017, 21:04 Linus Unnebäck, ***@***.***> wrote: In this specific case, I can imagine that the GameEngine sets up some kind of loop that runs every frame or similar. Instead of doing that in the constructor move that to a .start() function. e.g. old: class GameEngine { constructor () { // ... setInterval(() => this.renderFrame(), 1000 / 30) } // ... } // ... new GameEngine() new: class GameEngine { constructor () { // ... } start () { setInterval(() => this.renderFrame(), 1000 / 30) } // ... } // ... const engine = new GameEngine() engine.start() — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#958 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ABv6Rh6akfbblvU_645_Q9KtPhT805wkks5sTjNdgaJpZM4Oi1Ha> .

[LinusU]

The constructor it initialises variables with sensible defaults does that count as a side effect?

No, that is how it should be 👍

Side effects are something that affects anything outside of the class itself. So it's perfectly fine to modify anything that beings with this., but you shouldn't modify anything outside of the class.

setTimeout, setInterval, process.nextTick, .addEventListener, .requestAnimationFrame, etc. all implicitly modifies global state and we should always think really carefully before using them in a constructor.