JS实现数字千分位分隔

/**
 * @description: 数字千分位分隔
 * @param {number} num 传入的数字
 * @return {string}  reslute 返回结果
 */

function format(num) {
    let str = num.toString();
    if (str.length < 4) {
        return str;
    } else {
        let remainder = str.length % 3;
        //如果余数不为0  则不是3的整数倍
        if (remainder) {
            return str.slice(0, remainder) + "," + str.slice(remainder).match(/\d{3}/g).join(",");
        } else {
            return str.slice(remainder).match(/\d{3}/g).join(",");
        }
    }
}

console.log(format(1000000000));