How to use matching regularity, you can only enter numbers or negative numbers, but no matter positive or negative numbers only retain one decimal point.

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ask for advice
how to keep the attributes of input and number as decimal points, why can"t the negative sign (-) be entered

Javascript
Mar.08,2021 
let reg = /^-?\d+(\.\d)?$/
/**
 *
 * @param {String} input - 
 * @param {Integer} precision - 1
 * @param {String} type - numberstringundefined"number"
 * @returns {Number|String} type
 */
function demo(input, precision = 1, type = "number") {
    if (typeof input !== "string") {
        try {
            //,
            input = input.toString();
        } catch (error) {
            throw new Error("");
        }
        console.warn("string")
    }
    //precision
    if (!Number.isInteger(precision) || precision < 0) {
        throw new Error("");
    }
    //
    let isMatch = false;
    //:{0,1}?
    const reg = /^-{0,1}\d+(\.\d+){0,1}$/;
    //:replacereturnnumber replace
    const result = input.replace(reg, (match, floatPart) => {
        //true
        isMatch = true;
        //
        const intPart = Math.abs(parseInt(match));
        //,
        const symbol = match.startsWith("-") ? "-" : "";
        //0
        floatPart = floatPart ? parseFloat(parseFloat(floatPart).toFixed(precision)) : 0;
        // 
        return symbol + (intPart + floatPart);
    });
    //
    if (!isMatch) {
        throw new Error("");
    }
    //resulttype
    return type === "number" ? parseFloat(result) : result;
}

clipboard.png

/ ^ -? (([1-9]\ d * (\.\ d {1})? $) | (0\.\ d {1} $) | 0) $/

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