80 lines
2.3 KiB
JavaScript
80 lines
2.3 KiB
JavaScript
/**
|
|
* @license Apache-2.0
|
|
*
|
|
* Copyright (c) 2020 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( './../../is-string' ).isPrimitive;
|
|
var isNonNegativeInteger = require( './../../is-nonnegative-integer' ).isPrimitive;
|
|
|
|
|
|
// VARIABLES //
|
|
|
|
// Range for a high surrogate
|
|
var OxD800 = 0xD800|0; // 55296
|
|
var OxDBFF = 0xDBFF|0; // 56319
|
|
|
|
// Range for a low surrogate
|
|
var OxDC00 = 0xDC00|0; // 56320
|
|
var OxDFFF = 0xDFFF|0; // 57343
|
|
|
|
|
|
// MAIN //
|
|
|
|
/**
|
|
* Tests if a position in a string marks the start of a UTF-16 surrogate pair.
|
|
*
|
|
* @private
|
|
* @param {string} str - input string
|
|
* @param {NonNegativeInteger} pos - position in string
|
|
* @throws {TypeError} first argument must be a string primitive
|
|
* @throws {TypeError} second argument must be a nonnegative integer
|
|
* @throws {RangeError} position must be a valid index in string
|
|
* @returns {boolean} boolean indicating whether the string has a surrogate pair at a position
|
|
*
|
|
* @example
|
|
* var out = hasUTF16SurrogatePairAt( '🌷', 0 );
|
|
* // returns true
|
|
*
|
|
* @example
|
|
* var out = hasUTF16SurrogatePairAt( '🌷', 1 );
|
|
* // returns false
|
|
*/
|
|
function hasUTF16SurrogatePairAt( str, pos ) {
|
|
var ch1;
|
|
var ch2;
|
|
if ( !isString( str ) ) {
|
|
throw new TypeError( 'invalid argument. Must provide a string. Value: `' + str + '`.' );
|
|
}
|
|
if ( !isNonNegativeInteger( pos ) ) {
|
|
throw new TypeError( 'invalid argument. Must provide a valid position (nonnegative integer). Value: `' + pos + '`.' );
|
|
}
|
|
if ( pos >= str.length ) {
|
|
throw new RangeError( 'invalid argument. Must provide a valid position (within string bounds). Value: `' + pos + '`.' );
|
|
}
|
|
ch1 = str.charCodeAt( pos );
|
|
ch2 = str.charCodeAt( pos + 1 );
|
|
return ch1 >= OxD800 && ch1 <= OxDBFF && ch2 >= OxDC00 && ch2 <= OxDFFF;
|
|
}
|
|
|
|
|
|
// EXPORTS //
|
|
|
|
module.exports = hasUTF16SurrogatePairAt;
|