Spaceship Operator

[Isiah Meadows]

For what it's worth, for most practical purposes, `arr.sort((a, b) => b -
a))` works well enough. (The only thing it doesn't work well with are NaNs,
but in practice, those almost never occur.)

On Tue, Jun 27, 2017, 16:11 森建 <moriken at kimamass.com> wrote:

> PHP, Ruby, Groovy have spaceship operator `<=>`. In short, this operator
> compares values and returns `1`, `-1`, `0`.
>
> ECMAScript spec's `TypedArray#sort` has the default comparison part like
> following code, so I think it's useful that appending spaceship operator to
> ECMAScript like  it.
>
> http://www.ecma-international.org/ecma-262/8.0/#sec-%typedarray%.prototype.sort
>
> ```javascript
> function isPlusZero(val) {
>      return val === 0 && 1 / val === Infinity;
> }
>
> function defaultCompare(x, y) {
>      const [isNaN_x, isNaN_y] = [Number.isNaN(x), Number.isNaN(y)];
>
>      if(isNaN_x && isNaN_y)
>          return 0;
>
>      if(isNaN_x)
>          return 1;
>
>      if(isNaN_y)
>          return -1;
>
>      if(x < y)
>          return -1;
>
>      if(x > y)
>          return 1;
>
>      if(x === 0 && y === 0) {
>          const [isPlusZero_x, isPlusZero_y] = [isPlusZero(x),
> isPlusZero(y)];
>
>          if(!isPlusZero_x && isPlusZero_y)
>              return -1;
>
>          if(isPlusZero_x && !isPlusZero_y)
>              return 1;
>      }
>
>      return 0;
> }
> ```
>
> ```javascript
> // NaN behave like the biggest number
> NaN <=> NaN // 0
> NaN <=> 42 // 1
> 42 <=> NaN // -1
> Infinity <=> NaN // -1
>
> // finite
> 10 <=> 10 // 0
> -1 <=> 10 // -1
> 10 <=> -1 // 1
>
> // 0, -0 are not the same
> -0 <=> 0 // -1
> 0 <=> -0 // 1
> ```
>
> ## Use cases
>
> ```javascript
> // Array#sort can use TypedArray#sort default comparison part
> [10, 5, NaN, -1].sort((a, b) => a <=> b); // [-1, 5, 10, NaN]
>
> // desc order
> new Float64Array([10, 5, NaN, -1]).sort((a, b) => -(a <=> b)); // [NaN,
> 10, 5, -1]
> ```
>
> ## Problems
>
> `TypedArray#sort` default comparison part has no `string` order function.
>
> ```javascript
> "abc" <=> "def" // same as "abc".localeCompare("def") ?
> "abc" <=> 42 // same as "abc".localeCompare("42") ?
> ```
>
> I found the reference to spaceship operator in ES Discuss. It has Already
> discussed in TC39 meeting?
> https://esdiscuss.org/topic/informative-notes#content-3
> _______________________________________________
> es-discuss mailing list
> es-discuss at mozilla.org
> https://mail.mozilla.org/listinfo/es-discuss
>
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