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35 lines
1.0 KiB
35 lines
1.0 KiB
// 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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