梁美英 / programming · Files

// https://github.com/tc39/proposal-string-pad-start-end
var toLength = require('./_to-length')
  , repeat   = require('./_string-repeat')
  , defined  = require('./_defined');

module.exports = function(that, maxLength, fillString, left){
  var S            = String(defined(that))
    , stringLength = S.length
    , fillStr      = fillString === undefined ? ' ' : String(fillString)
    , intMaxLength = toLength(maxLength);
  if(intMaxLength <= stringLength || fillStr == '')return S;
  var fillLen = intMaxLength - stringLength
    , stringFiller = repeat.call(fillStr, Math.ceil(fillLen / fillStr.length));
  if(stringFiller.length > fillLen)stringFiller = stringFiller.slice(0, fillLen);
  return left ? stringFiller + S : S + stringFiller;
};