80 lines
2.3 KiB
JavaScript
80 lines
2.3 KiB
JavaScript
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/**
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* @license Apache-2.0
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*
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* Copyright (c) 2020 The Stdlib Authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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'use strict';
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// MODULES //
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var isString = require( './../../is-string' ).isPrimitive;
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var isNonNegativeInteger = require( './../../is-nonnegative-integer' ).isPrimitive;
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// VARIABLES //
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// Range for a high surrogate
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var OxD800 = 0xD800|0; // 55296
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var OxDBFF = 0xDBFF|0; // 56319
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// Range for a low surrogate
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var OxDC00 = 0xDC00|0; // 56320
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var OxDFFF = 0xDFFF|0; // 57343
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// MAIN //
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/**
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* Tests if a position in a string marks the start of a UTF-16 surrogate pair.
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*
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* @private
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* @param {string} str - input string
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* @param {NonNegativeInteger} pos - position in string
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* @throws {TypeError} first argument must be a string primitive
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* @throws {TypeError} second argument must be a nonnegative integer
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* @throws {RangeError} position must be a valid index in string
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* @returns {boolean} boolean indicating whether the string has a surrogate pair at a position
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*
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* @example
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* var out = hasUTF16SurrogatePairAt( '🌷', 0 );
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* // returns true
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*
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* @example
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* var out = hasUTF16SurrogatePairAt( '🌷', 1 );
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* // returns false
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*/
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function hasUTF16SurrogatePairAt( str, pos ) {
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var ch1;
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var ch2;
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if ( !isString( str ) ) {
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throw new TypeError( 'invalid argument. Must provide a string. Value: `' + str + '`.' );
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}
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if ( !isNonNegativeInteger( pos ) ) {
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throw new TypeError( 'invalid argument. Must provide a valid position (nonnegative integer). Value: `' + pos + '`.' );
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}
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if ( pos >= str.length ) {
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throw new RangeError( 'invalid argument. Must provide a valid position (within string bounds). Value: `' + pos + '`.' );
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}
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ch1 = str.charCodeAt( pos );
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ch2 = str.charCodeAt( pos + 1 );
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return ch1 >= OxD800 && ch1 <= OxDBFF && ch2 >= OxDC00 && ch2 <= OxDFFF;
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}
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// EXPORTS //
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module.exports = hasUTF16SurrogatePairAt;
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