Int to Roman(整数转为罗马数字)(1-3999999)

intToRoman.js

function convert(num) {
    // suppose num>0&&num<4000000
    if(!Number.isInteger(num)) {
        throw 'Sorry, there are only integers in Rome numerals.';
    } else if(num<0) {
        throw 'Sorry, there is no negative in Roman numerals.';
    } else if(num===0) {
        throw 'Sorry, there is no zero in Roman numerals.';
    } else if(num>=4000000) {
        throw 'Sorrt, 4000000 and more are too high.';
    }
    let numStr = num.toString(),
        len = numStr.length,
        numObj = [];
    for (let i = 0; i < len; i++) {
        numObj.push({
            weight: Math.pow(10, len - i - 1),
            value: parseInt(numStr[i])
        });
    }
    const romanObj = {
        '1': 'I',
        '5': 'V',
        '10': 'X',
        '50': 'L',
        '100': 'C',
        '500': 'D',
        '1000': 'M',
        '5000': 'V`',
        '10000': 'X`',
        '50000': 'L`',
        '100000': 'C`',
        '500000': 'D`',
        '1000000': 'M`',
    };
    let retStr = numObj.map(function (item) {
        switch (item.value) {
            case 0:
            case 1:
            case 2:
            case 3:
                return romanObj[item.weight.toString()].repeat(item.value);
            case 4:
            case 5:
                return romanObj[item.weight.toString()].repeat(5-item.value)+romanObj[5*item.weight.toString()];
            case 6:
            case 7:
            case 8:
                return romanObj[5*item.weight.toString()]+romanObj[item.weight.toString()].repeat(item.value-5);
            case 9:
                return romanObj[item.weight.toString()]+romanObj[10*item.weight.toString()];
        }
    }).join('');
    return retStr;
}

let x = convert(123);
console.log(x);