数值补全指定位数

function padNumber(num, fill) {
  var len = (‘‘ + num).length;
  return (Array(fill > len ? fill - len + 1 || 0 : 0).join(0) + num);
}

console.log(padNumber(11, 5)); // 00011

//允许负数

 
function padNumber(number, fill) {
var new_number = number * (number > 0 ? 1 : -1),
len = (‘‘ + new_number).length;
return (number > 0 ? ‘‘ : ‘-‘) + (Array(
fill > len ? fill - len + 1 || 0 : 0
).join(0) + new_number);
}

‘11‘.padStart(4, ‘0‘) // 0011

‘1‘.padEnd(5, ‘0‘) // 10000