JS字符串补全方法padStart()和padEnd()

str.padStart(targetLength [, padString])
str.padEnd(targetLength [, padString])

'abc'.padStart(1, 'd');     // "abc"
'abc'.padEnd(1, 'd');     // "abc"

'abc'.padStart(6,"123456");    // "123abc"
'abc'.padEnd(6, "123456");    // "abc123"

'abc'.padStart(10);     // "    abc"
'abc'.padEnd(10);     // "abc    "

'abc'.padStart(5, "foo");    // "foabc"
'abc'.padEnd(5, "foo");     // "abcfo"

function dataFormat(data) {
  const dt = new Date(data * 1000) //注：如果是13位时间戳不用*1000 
  
  const y = dt.getFullYear()
  const m = (dt.getMonth() + 1 + '').padStart(2, '0')
  const d = (dt.getDay() + '').padStart(2, '0')
​
  const hh = (dt.getHours() + '').padStart(2, '0')
  const mm = (dt.getMinutes() + '').padStart(2, '0')
  const ss = (dt.getSeconds() + '').padStart(2, '0')
​
  return `${y}-${m}-${d} ${hh}:${mm}:${ss}`
}

// https://github.com/uxitten/polyfill/blob/master/string.polyfill.js
// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/padEnd
if (!String.prototype.padEnd) {
  String.prototype.padEnd = function padEnd(targetLength,padString) {
    targetLength = targetLength>>0; //floor if number or convert non-number to 0;
    padString = String((typeof padString !== 'undefined' ? padString: ''));
    if (this.length > targetLength) {
      return String(this);
    }
    else {
      targetLength = targetLength-this.length;
      if (targetLength > padString.length) {
        padString += padString.repeat(targetLength/padString.length); //append to original to ensure we are longer than needed
      }
      return String(this) + padString.slice(0,targetLength);
    }
  };
}