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2d441493a4
PR-URL: https://github.com/nodejs/io.js/pull/2286 Reviewed-By: Roman Reiss <me@silverwind.io>
34 lines
1.0 KiB
JavaScript
34 lines
1.0 KiB
JavaScript
// Based on: https://github.com/mathiasbynens/String.prototype.at
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// Thanks @mathiasbynens !
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'use strict';
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var toInteger = require('../../number/to-integer')
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, validValue = require('../../object/valid-value');
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module.exports = function (pos) {
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var str = String(validValue(this)), size = str.length
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, cuFirst, cuSecond, nextPos, len;
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pos = toInteger(pos);
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// Account for out-of-bounds indices
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// The odd lower bound is because the ToInteger operation is
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// going to round `n` to `0` for `-1 < n <= 0`.
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if (pos <= -1 || pos >= size) return '';
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// Second half of `ToInteger`
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pos = pos | 0;
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// Get the first code unit and code unit value
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cuFirst = str.charCodeAt(pos);
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nextPos = pos + 1;
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len = 1;
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if ( // check if it’s the start of a surrogate pair
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(cuFirst >= 0xD800) && (cuFirst <= 0xDBFF) && // high surrogate
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(size > nextPos) // there is a next code unit
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) {
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cuSecond = str.charCodeAt(nextPos);
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if (cuSecond >= 0xDC00 && cuSecond <= 0xDFFF) len = 2; // low surrogate
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}
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return str.slice(pos, pos + len);
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};
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