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* @license Apache-2.0
*
* Copyright (c) 2025 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';
// MODULES //
var isString = require( '@stdlib/assert/is-string' ).isPrimitive;
var format = require( '@stdlib/string/format' );
// VARIABLES //
var RE_UTF16_LOW_SURROGATE = /[\uDC00-\uDFFF]/; // TODO: replace with stdlib pkg
var RE_UTF16_HIGH_SURROGATE = /[\uD800-\uDBFF]/; // TODO: replace with stdlib pkg
// MAIN //
/**
* Returns the number of code points in a string.
*
* @param {string} str - input string
* @throws {TypeError} must provide a string
* @returns {NonNegativeInteger} number of code points
*
* @example
* var out = numCodePoints( 'last man standing' );
* // returns 17
*
* @example
* var out = numCodePoints( 'presidential election' );
* // returns 21
*
* @example
* var out = numCodePoints( 'अनुच्छेद' );
* // returns 8
*/
function numCodePoints( str ) {
var count;
var i;
if ( !isString( str ) ) {
throw new TypeError( format( 'invalid argument. Must provide a string. Value: `%s`.', str ) );
}
count = 0;
// Process the string one Unicode code unit at a time and count UTF-16 surrogate pairs as a single Unicode code point...
for ( i = 0; i < str.length; i++ ) {
// Check for a high UTF-16 surrogate...
if ( RE_UTF16_HIGH_SURROGATE.test( str[ i ] ) ) {
// Check for an unpaired surrogate at the end of the input string...
if ( i === str.length-1 ) {
// We found an unpaired surrogate...
count += 1;
break;
}
// Check whether the high surrogate is paired with a low surrogate...
if ( RE_UTF16_LOW_SURROGATE.test( str[ i+1 ] ) ) {
// We found a surrogate pair:
i += 1; // bump the index to process the next code unit
count += 1;
}
} else {
count += 1;
}
}
return count;
}
// EXPORTS //
module.exports = numCodePoints;
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