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* @license Apache-2.0
*
* Copyright (c) 2024 The Stdlib Authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
'use strict';
// VARIABLES //
var RE_UTF16_LOW_SURROGATE = /[\uDC00-\uDFFF]/;
var RE_UTF16_HIGH_SURROGATE = /[\uD800-\uDBFF]/;
// MAIN //
/**
* Tests if a string is a well-formed string.
*
* @param {string} str - input string
* @returns {boolean} boolean indicating if a value is a well-formed string primitive
*
* @example
* var bool = isWellFormed( '' );
* // returns true
*
* @example
* var bool = isWellFormed( new String( '\uDC00' ) );
* // returns false
*/
function isWellFormed( str ) {
var i;
for ( i = 0; i < str.length; i++ ) {
// Checking if a low surrogate is present at the beginning
if ( i === 0 && RE_UTF16_LOW_SURROGATE.test(str[i]) ) {
return false;
}
// Checking if a high surrogate is present at the last position
if ( i === str.length - 1 && RE_UTF16_HIGH_SURROGATE.test(str[i]) ) {
return false;
}
// Checking if there is no low surrogate after a high surrogate
if ( i < str.length - 1 && RE_UTF16_HIGH_SURROGATE.test(str[i]) ) {
if ( RE_UTF16_LOW_SURROGATE.test(str[i + 1]) ) {
i += 1;
}
else {
return false;
}
}
// Checking if there is no high surrogate before a low surrogate
if ( i > 0 && RE_UTF16_LOW_SURROGATE.test(str[i]) ) {
if ( !RE_UTF16_HIGH_SURROGATE.test(str[i - 1]) ) {
return false;
}
}
}
return true;
}
// EXPORTS //
module.exports = isWellFormed;
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