### toDecimalMark

Use `toLocaleString()` to convert a float-point arithmetic to the [Decimal mark](https://en.wikipedia.org/wiki/Decimal_mark) form. It makes a comma separated string from a number.

 ```js
const toDecimalMark = num => num.toLocaleString('en-US');
// toDecimalMark(12305030388.9087) -> "12,305,030,388.9087"
```