aaac7fed
 liuqimichale
add
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// 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`
// eslint-disable-next-line no-bitwise
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);
};
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