51 lines
1.3 KiB
JavaScript
51 lines
1.3 KiB
JavaScript
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'use strict';
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var callBound = require('call-bind/callBound');
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var $TypeError = require('es-errors/type');
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var $charAt = callBound('String.prototype.charAt');
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var isString = require('is-string');
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var isNegativeZero = require('is-negative-zero');
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var unbox = require('unbox-primitive');
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var CanonicalNumericIndexString = require('./CanonicalNumericIndexString');
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var IsInteger = require('./IsInteger');
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var IsPropertyKey = require('./IsPropertyKey');
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// https://262.ecma-international.org/6.0/#sec-stringgetindexproperty
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module.exports = function StringGetIndexProperty(S, P) {
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if (typeof S === 'string' || !isString(S)) {
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throw new $TypeError('Assertion failed: `S` must be a boxed String Object');
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}
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if (!IsPropertyKey(P)) {
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throw new $TypeError('Assertion failed: `P` must be a Property Key');
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}
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if (typeof P !== 'string') {
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return void undefined;
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}
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var index = CanonicalNumericIndexString(P);
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if (typeof index === 'undefined' || !IsInteger(index) || isNegativeZero(index)) {
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return void undefined;
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}
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var str = unbox(S);
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var len = str.length;
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if (index < 0 || len <= index) {
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return void undefined;
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}
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var resultStr = $charAt(str, index);
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return {
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'[[Configurable]]': false,
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'[[Enumerable]]': true,
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'[[Value]]': resultStr,
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'[[Writable]]': false
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};
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};
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