107 lines
2.9 KiB
JavaScript
107 lines
2.9 KiB
JavaScript
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/**
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* @license Apache-2.0
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*
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* Copyright (c) 2018 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 isInteger = require( '@stdlib/assert/is-integer' ).isPrimitive;
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var isString = require( '@stdlib/assert/is-string' ).isPrimitive;
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var format = require( './../../format' );
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// MAIN //
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/**
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* Tests if a string starts with the characters of another string.
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*
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* @param {string} str - input string
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* @param {string} search - search string
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* @param {integer} [position=0] - position at which to start searching
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* @throws {TypeError} first argument must be a string
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* @throws {TypeError} second argument must be a string
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* @throws {TypeError} third argument must be an integer
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* @returns {boolean} boolean indicating if the input string starts with the search string
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*
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* @example
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* var bool = startsWith( 'Remember the story I used to tell you when you were a boy?', 'Remember' );
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* // returns true
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*
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* @example
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* var bool = startsWith( 'Remember the story I used to tell you when you were a boy?', 'Remember, remember' );
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* // returns false
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*
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* @example
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* var bool = startsWith( 'To be, or not to be, that is the question.', 'To be' );
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* // returns true
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*
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* @example
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* var bool = startsWith( 'To be, or not to be, that is the question.', 'to be' );
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* // returns false
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*
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* @example
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* var bool = startsWith( 'To be, or not to be, that is the question.', 'to be', 14 );
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* // returns true
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*
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* @example
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* var bool = startsWith( 'To be, or not to be, that is the question.', 'quest', -9 );
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* // returns true
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*/
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function startsWith( str, search, position ) {
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var pos;
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var i;
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if ( !isString( str ) ) {
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throw new TypeError( format( 'invalid argument. First argument must be a string. Value: `%s`.', str ) );
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}
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if ( !isString( search ) ) {
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throw new TypeError( format( 'invalid argument. Second argument must be a string. Value: `%s`.', search ) );
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}
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if ( arguments.length > 2 ) {
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if ( !isInteger( position ) ) {
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throw new TypeError( format( 'invalid argument. Third argument must be an integer. Value: `%s`.', position ) );
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}
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if ( position < 0 ) {
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pos = str.length + position;
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} else {
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pos = position;
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}
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} else {
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pos = 0;
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}
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if ( search.length === 0 ) {
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return true;
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}
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if (
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pos < 0 ||
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pos + search.length > str.length
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) {
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return false;
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}
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for ( i = 0; i < search.length; i++ ) {
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if ( str.charCodeAt( pos + i ) !== search.charCodeAt( i ) ) {
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return false;
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}
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}
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return true;
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}
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// EXPORTS //
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module.exports = startsWith;
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