36 lines
1.0 KiB
JavaScript
36 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, 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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// eslint-disable-next-line no-bitwise
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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 (
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// Check if it’s the start of a surrogate pair
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cuFirst >= 0xd800 &&
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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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