59 lines
1.7 KiB
JavaScript
59 lines
1.7 KiB
JavaScript
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'use strict';
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var GetIntrinsic = require('get-intrinsic');
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var $TypeError = GetIntrinsic('%TypeError%');
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var callBound = require('call-bind/callBound');
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var isLeadingSurrogate = require('../helpers/isLeadingSurrogate');
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var isTrailingSurrogate = require('../helpers/isTrailingSurrogate');
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var Type = require('./Type');
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var UTF16SurrogatePairToCodePoint = require('./UTF16SurrogatePairToCodePoint');
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var $charAt = callBound('String.prototype.charAt');
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var $charCodeAt = callBound('String.prototype.charCodeAt');
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// https://262.ecma-international.org/12.0/#sec-codepointat
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module.exports = function CodePointAt(string, position) {
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if (Type(string) !== 'String') {
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throw new $TypeError('Assertion failed: `string` must be a String');
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}
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var size = string.length;
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if (position < 0 || position >= size) {
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throw new $TypeError('Assertion failed: `position` must be >= 0, and < the length of `string`');
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}
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var first = $charCodeAt(string, position);
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var cp = $charAt(string, position);
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var firstIsLeading = isLeadingSurrogate(first);
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var firstIsTrailing = isTrailingSurrogate(first);
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if (!firstIsLeading && !firstIsTrailing) {
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return {
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'[[CodePoint]]': cp,
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'[[CodeUnitCount]]': 1,
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'[[IsUnpairedSurrogate]]': false
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};
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}
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if (firstIsTrailing || (position + 1 === size)) {
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return {
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'[[CodePoint]]': cp,
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'[[CodeUnitCount]]': 1,
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'[[IsUnpairedSurrogate]]': true
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};
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}
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var second = $charCodeAt(string, position + 1);
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if (!isTrailingSurrogate(second)) {
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return {
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'[[CodePoint]]': cp,
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'[[CodeUnitCount]]': 1,
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'[[IsUnpairedSurrogate]]': true
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};
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}
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return {
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'[[CodePoint]]': UTF16SurrogatePairToCodePoint(first, second),
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'[[CodeUnitCount]]': 2,
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'[[IsUnpairedSurrogate]]': false
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};
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};
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