If you don't want to think about having to call functions each time, you can create a Class that handles conversion for you.
class Decimal {
constructor(value = 0, scale = 4) {
this.intervalValue = value;
this.scale = scale;
}
get value() {
return this.intervalValue;
}
set value(value) {
this.intervalValue = Decimal.toDecimal(value, this.scale);
}
static toDecimal(val, scale) {
const factor = 10 ** scale;
return Math.round(val * factor) / factor;
}
}
Usage:
const d = new Decimal(0, 4);
d.value = 0.1 + 0.2; // 0.3
d.value = 0.3 - 0.2; // 0.1
d.value = 0.1 + 0.2 - 0.3; // 0
d.value = 5.551115123125783e-17; // 0
d.value = 1 / 9; // 0.1111
Of course, when dealing with Decimal there are caveats:
d.value = 1/3 + 1/3 + 1/3; // 1
d.value -= 1/3; // 0.6667
d.value -= 1/3; // 0.3334
d.value -= 1/3; // 0.0001
You'd ideally want to use a high scale (like 12), and then convert it down when you need to present it or store it somewhere. Personally, I did experiment with creating a UInt8Array and trying to create a precision value (much like the SQL Decimal type), but since Javascript doesn't let you overload operators, it just gets a bit tedious not being able to use basic math operators (+, -, /, *) and using functions instead like add(), substract(), mult(). For my needs, it's not worth it.
But if you do need that level of precision and are willing to endure the use of functions for math, then I recommend the decimal.js library.