git.r.bdr.sh - rbdr/dotfiles/blob

   1 // Based on: https://github.com/mathiasbynens/String.prototype.at
   2 // Thanks @mathiasbynens !
   3
   4 'use strict';
   5
   6 var toInteger  = require('../../number/to-integer')
   7   , validValue = require('../../object/valid-value');
   8
   9 module.exports = function (pos) {
  10         var str = String(validValue(this)), size = str.length
  11           , cuFirst, cuSecond, nextPos, len;
  12         pos = toInteger(pos);
  13
  14         // Account for out-of-bounds indices
  15         // The odd lower bound is because the ToInteger operation is
  16         // going to round `n` to `0` for `-1 < n <= 0`.
  17         if (pos <= -1 || pos >= size) return '';
  18
  19         // Second half of `ToInteger`
  20         pos = pos | 0;
  21         // Get the first code unit and code unit value
  22         cuFirst = str.charCodeAt(pos);
  23         nextPos = pos + 1;
  24         len = 1;
  25         if ( // check if it’s the start of a surrogate pair
  26                 (cuFirst >= 0xD800) && (cuFirst <= 0xDBFF) && // high surrogate
  27                         (size > nextPos) // there is a next code unit
  28         ) {
  29                 cuSecond = str.charCodeAt(nextPos);
  30                 if (cuSecond >= 0xDC00 && cuSecond <= 0xDFFF) len = 2; // low surrogate
  31         }
  32         return str.slice(pos, pos + len);
  33 };