mirror of https://github.com/lukechilds/node.git
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
33 lines
1.0 KiB
33 lines
1.0 KiB
// 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);
|
|
};
|
|
|