Can I use variables in JS `e` numbers?-CodePudding

Per 'e' in javascript numbers I would like to use 'e' notation:

Right now I'm doing:

const USD_DECIMALS = 2
const USD = 1e2

As you can see I'm duplicating the number 2. When I'd like to do is something like:

const USD_DECIMALS = 2
const USD = 1e[USD_DECIMALS]

Is this possible? Maybe using the Number() constructor or similar?

CodePudding user response：

You could make a string out of "1e2" and then run it through Number.

const USD_DECIMALS = 2
const USDString = `1e${USD_DECIMALS}`;
const USD = Number(USDString);

console.log(USD);

CodePudding user response：

Not directly (without building a dynamic string, but then that's not direct either), but since 1e2 means 1 times 10², you can use either 1 * Math.pow(10, USD_DECIMALS) OR 1 * 10**USD_DECIMALS to do the same thing dynamically:

const USD_DECIMALS = 2;
const USD = 1 * 10**USD_DECIMALS;
// Or: const USD = 1 * Math.pow(10, USD_DECIMALS);

Live Example:

console.log("Various ways to get 10²:");
console.log(1e2);
const USD_DECIMALS = 2;
console.log(1 * Math.pow(10, USD_DECIMALS));
console.log(1 * 10**USD_DECIMALS);

console.log("Just for completeness, 10³:");
console.log(1e3);
const USD_DECIMALS3 = 3;
console.log(1 * Math.pow(10, USD_DECIMALS3));
console.log(1 * 10**USD_DECIMALS3);

.as-console-wrapper {
    max-height: 100% !important;
}

(Side note: you sometimes need () around ** expressions where you may not expect to, such as in -1 ** 10, but not in the above.)

CodePudding user response：

The NeM is for the order of magnitude (N*10^M). What you can do is just

n=n*(10**m)

If you actually want to control the number of decimals you have to round.