inconsistent formation number with numeric separator

[alexander-akait]

Prettier 2.0.5
Playground link

--parser babel

Input:

const number = 1_000_000.000;
const number = 1_000_000.0_0_0;

Output:

const number = 1_000_000.0;
const number = 1_000_000.0_0_0;

Expected behavior:

const number = 1_000_000.0;
const number = 1_000_000.0;

Will be great to hear other opinions.

[Skalman]

I think I'd prefer Prettier not to modify numbers with numeric separators at all. Using a numeric separator at all is a type of manual formatting, and I don't see how Prettier can determine what was meant originally.

I'd prefer the following not to be reformatted at all:

const number = 1_000_000.000;
const number = 1_000_000.0_0_0;
const number = 1_000_000.0_0_1;
const number = 1_000_000.0_0_2;

[fisker]

But we format

const number = 1000000.0;
const number = 1000000.000;
const number = 1000000.001;
const number = 1000000.002;

[thorn0]

@fisker The difference is that there is no separators in your examples.

[sgregson]

I feel the same as @Skalman, I'd prefer prettier not format numeric separators. By way of example, the https://github.com/tc39/proposal-numeric-separator proposal's motivation demonstrate some common use cases for variable in placement of numeric separators, particularly around storing currency information without floating point numbers:

1_000_000_000           // Ah, so a billion
101_475_938.38          // And this is hundreds of millions

let fee = 123_00;       // $123 (12300 cents, apparently)
let fee = 12_300;       // $12,300 (woah, that fee!)
let amount = 12345_00;  // 12,345 (1234500 cents, apparently)
let amount = 123_4500;  // 123.45 (4-fixed financial)
let amount = 1_234_500; // 1,234,500

The ability to place the separator intentionally at either the 3rd (currency), 4th (standard thousands), or 5th character (4-fixed financial) left of the decimal feels important to preserve.

[yoyo837]

Waiting for this feature.

[ELI7VH]

this should be a feauture. Myself, and many projects that I am on also would find it useful.

I don't see the big deal here, because a few people say "i don't want prettier to do this", then just simply don't enable it - why is this an argument.

The fact is there are certain projects and teams that would like this feature, and it is indeed a formatting issue - which, unless I am mistaken is the job of something like Prettier, is it not?

Everybody is throwing edge cases around, but why not just add an easy way to format it..

{
  "numeric_formatting": "(x)_###.###"
}

this would put an underscore after every 3rd digit, and retain a zero padding of N digits.

the syntax seems fairly simple and straightforward, and could probably cover most use cases.