antlr4/src/antlr4/polyfills/codepointat.js

JavaScript runtime for ANTLR4

/* Copyright (c) 2012-2022 The ANTLR Project Contributors. All rights reserved.
 * Use is of this file is governed by the BSD 3-clause license that
 * can be found in the LICENSE.txt file in the project root.
 */
/*! https://mths.be/codepointat v0.2.0 by @mathias */
if (!String.prototype.codePointAt) {
	(function() {
		'use strict'; // needed to support `apply`/`call` with `undefined`/`null`
		var defineProperty = (function() {
			// IE 8 only supports `Object.defineProperty` on DOM elements
			let result;
			try {
				const object = {};
				const $defineProperty = Object.defineProperty;
				result = $defineProperty(object, object, object) && $defineProperty;
			} catch(error) {
				/* eslint no-empty: [ "off" ] */
			}
			return result;
		}());
		const codePointAt = function(position) {
			if (this == null) {
				throw TypeError();
			}
			const string = String(this);
			const size = string.length;
			// `ToInteger`
			let index = position ? Number(position) : 0;
			if (index !== index) { // better `isNaN`
				index = 0;
			}
			// Account for out-of-bounds indices:
			if (index < 0 || index >= size) {
				return undefined;
			}
			// Get the first code unit
			const first = string.charCodeAt(index);
			let second;
			if ( // check if it’s the start of a surrogate pair
				first >= 0xD800 && first <= 0xDBFF && // high surrogate
				size > index + 1 // there is a next code unit
			) {
				second = string.charCodeAt(index + 1);
				if (second >= 0xDC00 && second <= 0xDFFF) { // low surrogate
					// https://mathiasbynens.be/notes/javascript-encoding#surrogate-formulae
					return (first - 0xD800) * 0x400 + second - 0xDC00 + 0x10000;
				}
			}
			return first;
		};
		if (defineProperty) {
			defineProperty(String.prototype, 'codePointAt', {
				'value': codePointAt,
				'configurable': true,
				'writable': true
			});
		} else {
			String.prototype.codePointAt = codePointAt;
		}
	}());
}

const CodePointAt = String.prototype.codePointAt;
export default CodePointAt;