StringGetIndexProperty.js

'use strict';

var GetIntrinsic = require('get-intrinsic');
var callBound = require('call-bind/callBound');

var $TypeError = GetIntrinsic('%TypeError%');

var $charAt = callBound('String.prototype.charAt');

var isString = require('is-string');
var isNegativeZero = require('is-negative-zero');
var unbox = require('unbox-primitive');

var CanonicalNumericIndexString = require('./CanonicalNumericIndexString');
var IsInteger = require('./IsInteger');
var IsPropertyKey = require('./IsPropertyKey');
var Type = require('./Type');

// https://262.ecma-international.org/6.0/#sec-stringgetindexproperty

module.exports = function StringGetIndexProperty(S, P) {
	if (typeof S === 'string' || !isString(S)) {
		throw new $TypeError('Assertion failed: `S` must be a boxed String Object');
	}
	if (!IsPropertyKey(P)) {
		throw new $TypeError('Assertion failed: `P` must be a Property Key');
	}

	if (Type(P) !== 'String') {
		return void undefined;
	}

	var index = CanonicalNumericIndexString(P);
	if (typeof index === 'undefined' || !IsInteger(index) || isNegativeZero(index)) {
		return void undefined;
	}

	var str = unbox(S);
	var len = str.length;
	if (index < 0 || len <= index) {
		return void undefined;
	}

	var resultStr = $charAt(str, index);

	return {
		'[[Configurable]]': false,
		'[[Enumerable]]': true,
		'[[Value]]': resultStr,
		'[[Writable]]': false
	};
};