JavaScript 实现字符串前补零的两种方法

/**
 * 前补0操作
 * @param number String 待操作字符串
 * @param length int 目标长度
 */
function addZero(number, length) {
  var buffer = "";
  if (number == "") {
    for (var i = 0; i < length; i ++) {
      buffer += "0";
    }
  } else {
    if (length < number.length) {
      return "";
    } else if (length == number.length) {
      return number;
    } else {
      for (var i = 0; i < (length - number.length); i ++) {
        buffer += "0";
      }
      buffer += number;
    }
  }
  return buffer;
}

function addZero(str,length){        
  return new Array(length - str.length + 1).join("0") + str;
}