node_modules/es5-ext/string/#/at.js

// Based on: https://github.com/mathiasbynens/String.prototype.at

// Thanks @mathiasbynens !

'use strict';

var toInteger  = require('../../number/to-integer')

  , validValue = require('../../object/valid-value');

module.exports = function (pos) {

    var str = String(validValue(this)), size = str.length

      , cuFirst, cuSecond, nextPos, len;

    pos = toInteger(pos);

    // Account for out-of-bounds indices

    // The odd lower bound is because the ToInteger operation is

    // going to round `n` to `0` for `-1 < n <= 0`.

    if (pos <= -1 || pos >= size) return '';

    // Second half of `ToInteger`

    pos = pos | 0;

    // Get the first code unit and code unit value

    cuFirst = str.charCodeAt(pos);

    nextPos = pos + 1;

    len = 1;

    if ( // check if it’s the start of a surrogate pair

        (cuFirst >= 0xD800) && (cuFirst <= 0xDBFF) && // high surrogate

            (size > nextPos) // there is a next code unit

    ) {

        cuSecond = str.charCodeAt(nextPos);

        if (cuSecond >= 0xDC00 && cuSecond <= 0xDFFF) len = 2; // low surrogate

    }

    return str.slice(pos, pos + len);

};