text: 'use strict';
  module.exports = leftPad;
  
  var cache = ['', ' ', '  ', '   ', '    ', '     ', '      ', '       ', '        ', '         '];
  
  function leftPad(str, len, ch) {
    // convert `str` to `string`
    str = str + '';
    // `len` is the `pad`'s length now
    len = len - str.length;
    // doesn't need to pad
    if (len <= 0) return str;
    // `ch` defaults to `' '`
    if (!ch && ch !== 0) ch = ' ';
    // convert `ch` to `string`
    ch = ch + '';
    // cache common use cases
    if (ch === ' ' && len < 10) return cache[len] + str;
    // `pad` starts with an empty string
    var pad = '';
    // loop
    while (true) {
      // add `ch` to `pad` if `len` is odd
      if (len & 1) pad += ch;
      // devide `len` by 2, ditch the fraction
      len >>= 1;
      // "double" the `ch` so this operation count grows logarithmically on `len`
      // each time `ch` is "doubled", the `len` would need to be "doubled" too
      // similar to finding a value in binary search tree, hence O(log(n))
      if (len) ch += ch;
      else
        // `len` is 0, exit the loop
        break;
    }
    // pad `str`!
    return pad + str;
  }
  