Use-Cases of this tutorial
Numeric separators can be used to improve readability of large numbers. For example the number 111111111111111111111111, which is difficult to read, can be alternately written as 111_111_111_111_111_111_111_111
// Developer can read this number incorrectly and this may lead to bugs var n = 2565648775657678;
// difficult to read let a = BigInt(99999999999999999999);
These separators can be used in appropriate places, for example, digits can be grouped per thousand.
// This is much easier to read var n = 2_565_648_775_657_678;
let a = BigInt(99_999_999_999_999_999_999);
Obviously numeric separators are just for code readability, and will not change the value of the number.
Usage of numeric separators are bound to some limitations :
Multiple underscores cannot be included one after the other.
// not allowed var a = 4554__88978_6;
Underscore cannot be included at the end of the number.
// not allowed var a = 1111111111111111_;
Underscores cannot be included after a leading 0.
// not allowed var a = 0_333333333333;