JS给字符串指定位置打码

利用JS将手机号中间四位变成*号
给邮箱和手机号码打码这种功能一般都是后台来做，不建议用前端做

示例

maskString('13878822602', 2);     // => '13*********'
maskString('13878822602', 3, 4);  // => '138****2602'
maskString('13878822602', 3, 4, 'x');  // => '138xxxx2602'

/**
 * 判断一个变量是否为数值
 * @param {any} value 需要判断的值
 * @param {boolean} isLoose 是否可包含NaN或无限
 * @returns {boolean}
 *
 * isNum(999);             // => true;
 * isNum(0.1);             // => true;
 * isNum(NaN);             // => false;
 * isNum(NaN, true);       // => true;
 * isNum(Infinity);        // => false;
 * isNum(Infinity, true);  // => true;
 * isNum('abc');           // => false;
 * isNum('abc', true);     // => false;
 */
function isNum(value, isLoose) {
  const isNumType = typeof value === "number";
  if (isLoose) return isNumType;
  return isNumType && !Number.isNaN(value) && Number.isFinite(value);
}

/**
 * 判断一个变量是否为字符串
 * @param {*} value
 * @returns {boolean}
 */
function isStr(value) {
  return typeof value === "string";
}

/**
 * 判断一个变量是否为undefined
 * @param {*} value
 * @returns {boolean}
 */
function isUdf(value) {
  return value === undefined;
}

/**
 * 给字符串指定位置打码
 * @param {string} string 需要打码字符串
 * @param {number} start 开始位置
 * @param {number} length 打码长度
 * @param {string} mask 打码符号，默认: *
 * @returns {string}
 *
 * @example
 * maskString('13878822602', 2);     // => '13*********'
 * maskString('13878822602', 3, 4);  // => '138****2602'
 * maskString('13878822602', 3, 4, 'x');  // => '138xxxx2602'
 */
function maskString(string, start, length, mask) {
  const str = String(string);
  if (!isNum(start)) return str;
  if (isStr(length)) {
    mask = length;
    length = undefined;
  }
  if (!isStr(mask)) mask = "*";
  const maskStr = str
    .substr(start, length)
    .replace(/[^\u4e00-\u9fa5]/gm, mask)
    .replace(/[\u4e00-\u9fa5]/gm, mask + mask);
  const prefix = str.substr(0, start);
  const suffix = isUdf(length) ? "" : str.substr(start + length);
  return prefix + maskStr + suffix;
}