number-as-string/dist/scale-down.js

Precise number scaling and formatting without JavaScript floating-point precision issues

import { scientificToNumberString } from "./utils";
/**
 * Formats a scaled number string to a number string with the specified number of decimal places.
 *
 * @param scaledValue - The scaled number string to format.
 * @param decimals - The number of decimal places to include in the formatted number string.
 * @returns The formatted number string.
 */
export function scaleDown(scaledValue, decimals) {
    if (decimals < 0) {
        throw new Error("Decimals must be a non-negative integer");
    }
    let strValue = scaledValue.toString().toLowerCase();
    if (["infinity", "-infinity", "nan"].includes(strValue)) {
        throw new Error("Invalid scaledValue value");
    }
    if (strValue.startsWith("0x")) {
        strValue = BigInt(strValue).toString();
    }
    else if (strValue.includes("e")) {
        strValue = scientificToNumberString(strValue);
    }
    let [integerPart, fractionalPart = ""] = strValue.split(".");
    const sign = integerPart.startsWith("-") ? "-" : "";
    integerPart = sign
        ? integerPart.slice(1).replace(/^0+/, "") || "0"
        : integerPart.replace(/^0+/, "") || "0";
    fractionalPart = fractionalPart.replace(/0+$/, "");
    if (integerPart.length <= decimals) {
        return `${sign}0.${integerPart.padStart(decimals, "0")}${fractionalPart}`;
    }
    else {
        const trimmedFractionalPart = `${integerPart.slice(integerPart.length - decimals)}${fractionalPart}`.replace(/0+$/, "");
        integerPart = integerPart.slice(0, integerPart.length - decimals);
        if (trimmedFractionalPart.length === 0) {
            return `${sign}${integerPart}`;
        }
        return `${sign}${integerPart}.${trimmedFractionalPart.replace(/\.$/, "")}`;
    }
}
scaleDown("555555555555555555", 18);
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