46 lines
1.2 KiB
JavaScript
46 lines
1.2 KiB
JavaScript
'use strict';
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var GetIntrinsic = require('../GetIntrinsic');
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var IsInteger = require('./IsInteger');
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var Type = require('./Type');
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var MAX_SAFE_INTEGER = require('../helpers/maxSafeInteger');
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var $TypeError = GetIntrinsic('%TypeError%');
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var $charCodeAt = require('../helpers/callBound')('String.prototype.charCodeAt');
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// https://ecma-international.org/ecma-262/6.0/#sec-advancestringindex
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module.exports = function AdvanceStringIndex(S, index, unicode) {
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if (Type(S) !== 'String') {
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throw new $TypeError('Assertion failed: `S` must be a String');
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}
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if (!IsInteger(index) || index < 0 || index > MAX_SAFE_INTEGER) {
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throw new $TypeError('Assertion failed: `length` must be an integer >= 0 and <= 2**53');
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}
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if (Type(unicode) !== 'Boolean') {
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throw new $TypeError('Assertion failed: `unicode` must be a Boolean');
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}
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if (!unicode) {
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return index + 1;
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}
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var length = S.length;
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if ((index + 1) >= length) {
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return index + 1;
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}
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var first = $charCodeAt(S, index);
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if (first < 0xD800 || first > 0xDBFF) {
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return index + 1;
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}
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var second = $charCodeAt(S, index + 1);
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if (second < 0xDC00 || second > 0xDFFF) {
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return index + 1;
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}
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return index + 2;
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};
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