1000000000   // Is this a billion? a hundred millions? Ten millions?
101475938.38 // what scale is this? what power of 10?

const FEE = 12300;
// is this 12,300? Or 123, because it's in cents?

const AMOUNT = 1234500;
// is this 1,234,500? Or cents, hence 12,345? Or financial, 4-fixed 123.45?

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

0.000001 // 1 millionth
0.000_001 // 1 millionth
.000_001 // 1 millionth
-.000_001 // 1 millionth
1e10_000  // 10^10000 -- granted, far less useful / in-range...

let nibbles = 0b1010_0001_1000_0101;
let message = 0xA0_B0_C0;

let x1 = _52;              // This is an identifier, not a numeric literal
let x2 = 5_2;              // OK (decimal literal)

let x7 = 0x5_2;            // OK (hexadecimal literal)
0xff
0xdead_beef

0o52
0O52

0xa
0Xa
0XA
0xA

0n
2n
20n
2_0n
2_00n
2_0_0n
20_0n
-20_0n