core-js/modules/$.string-pad.js

Standard library

// https://github.com/ljharb/proposal-string-pad-left-right
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)return S;
  if(fillStr == '')fillStr = ' ';
  var fillLen = intMaxLength - stringLength
    , stringFiller = repeat.call(fillStr, Math.ceil(fillLen / fillStr.length));
  if(stringFiller.length > fillLen)stringFiller = left
    ? stringFiller.slice(stringFiller.length - fillLen)
    : stringFiller.slice(0, fillLen);
  return left ? stringFiller + S : S + stringFiller;
};