String.prototype.zpadStart

[Sunny Fu]

String.prototype.zpadStart = function (targetLength, padString) {
    let string = this
    while (string.length < targetLength) {
        string = padString + string
    }
    return string
}
const res = 'abc'.padStart(8, "0");

[kangkang123269]

String.prototype.zpadStart = function (length, char = '0') {
  let str = this;
  if (str.length >= length) {
    return str;
  }
  const diff = length - str.length;
  const padding = char.repeat(diff);
  return padding + str;
};