Convert A nested else if statement in to a switch statement in JavaScript

Question

I have the following endpoint with a nested (if) else if statement

@Patch("/games/:id")
  @HttpCode(200)
  async updateGame(@Param("id") id: number, @Body() update: Partial<Game>) {

    const updatedGame = await Game.findOne(id);
    if (!updatedGame) {
      throw new NotFoundError("HTTP 404 Not Found: No Games Here");
    } else if (update.color && !validColor(update.color)) {
      throw new BadRequestError("HTTP 400 Bad Request: No Such Color");
    } else if (
      update.board !== undefined &&
      moves(update.board, updatedGame.board) > 1
    ) {
      throw new BadRequestError(
        "HTTP 400 Bad Request:  Only one move allowed. Wait your turn"
      );
    } else {
      console.log("Game has been updated");
      return Game.merge(updatedGame, update).save();
    }
  }

And I would like to convert it to a switch statement for readability I've tried several attempts but somehow the values of the constant variables aren't being read.

the following is my switch statement attempt to replace the else if list

switch(updatedGame){
  case (!updatedGame):
  throw new NotFoundError("HTTP 404 Not Found: No Games Here")
  case(update.color && !validColor(update.color)):
  throw new BadRequestError("HTTP 400 Bad Request: No Such Color")
  case(update.board !== undefined && moves(update.board, updatedGame.board) > 1):
  throw new BadRequestError("HTTP 400 Bad Request:  Only one move allowed. Wait your turn")
  default : console.log("Game has been updated");
   Game.merge(updatedGame, update).save();


}

the if else if list work as it should but the switch statement gives errors

Why do you really need to change? ...and of course it errors, as the argument in your switch is what the case evaluates, and how can it with e.g. ´case(update.color && !validColor(update.color))´ when neither is related to updateGame? — Asons
– Asons, Commented Jul 7, 2018 at 19:23
That doesn't make any sense as a switch, they're not all taking the same result in the conditional. — jonrsharpe
– jonrsharpe, Commented Jul 7, 2018 at 19:25
@NinaScholz If I don't then the values provided aren't being updated in the database Game.merge(updatedGame, update).save — newDev
– newDev, Commented Jul 7, 2018 at 19:26
@LGSon, mainly for readability. I find switch statements very readable but I suck at writing them. — newDev
– newDev, Commented Jul 7, 2018 at 19:27

Tieson T. · Accepted Answer · 2018-07-07 19:29:20Z

3

For better readability, you could omit the else parts, because a thrown exception, which is not caught inside of the function ends the function.

if (!updatedGame) {
    throw new NotFoundError("HTTP 404 Not Found: No Games Here");
}
if (update.color && !validColor(update.color)) {
    throw new BadRequestError("HTTP 400 Bad Request: No Such Color");
}
if (update.board !== undefined && moves(update.board, updatedGame.board) > 1) {
    throw new BadRequestError("HTTP 400 Bad Request:  Only one move allowed. Wait your turn");
}
console.log("Game has been updated");
return Game.merge(updatedGame, update).save();

edited Jul 7, 2018 at 19:29

Tieson T.

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answered Jul 7, 2018 at 19:26

Nina Scholz

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3 Comments

Vivek Over a year ago

How does this improve readability? Please explain. Code given with if..else in question is more readable then this.

Nina Scholz Over a year ago

it is the early exit paradigm with single if. after an exit by exception or simply a return statement, nothing more happens.

newDev Over a year ago

Ah, okay, that makes sense! I somehow figured a switch statement would be cleaner. I guess that wouldn't be best practice Your code makes more sense and looks a lot cleaner! Thanks!

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