82 lines
2.1 KiB
JavaScript
82 lines
2.1 KiB
JavaScript
/**
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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 isDateObject = require( './../../is-date-object' );
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var isInteger = require( './../../is-integer' ).isPrimitive;
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// MAIN //
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/**
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* Tests whether a value corresponds to a leap year in the Gregorian calendar.
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*
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* ## Notes
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*
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* - According to the Gregorian calendar, every year that is exactly divisible by `4` is a leap year, except those years which are also divisible by `100` and not by `400` (e.g., `1900`).
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*
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* @param {*} [value] - input value
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* @returns {boolean} boolean whether a value corresponds to a leap year
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*
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* @example
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* var bool = isLeapYear();
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* // returns <boolean>
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*
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* @example
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* var bool = isLeapYear( new Date() );
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* // returns <boolean>
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*
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* @example
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* var bool = isLeapYear( 1996 );
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* // returns true
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*
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* @example
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* var bool = isLeapYear( 2001 );
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* // returns false
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*/
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function isLeapYear( value ) {
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var yr;
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if ( arguments.length ) {
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if ( isDateObject( value ) ) {
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yr = value.getFullYear();
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} else if ( isInteger( value ) ) {
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yr = value;
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} else {
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return false;
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}
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} else {
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// Note: cannot cache, as possible for application to cross into a new year:
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yr = ( new Date() ).getFullYear();
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}
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// Special case if year is a new century...
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if ( (yr % 100) === 0 ) {
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// Centuries are only leap years at the end of "leap cycles" which happen every `400` years:
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return ( (yr % 400) === 0 );
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}
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// All other years which are exactly divisible by `4` are leap years:
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return ( (yr % 4) === 0 );
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}
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// EXPORTS //
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module.exports = isLeapYear;
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