| var isDate = require('../lang/isDate');    /**     * checks if it's a leap year     */    function isLeapYear(fullYear){        if (isDate(fullYear)) {            fullYear = fullYear.getFullYear();        }        return fullYear % 400 === 0 || (fullYear % 100 !== 0 && fullYear % 4 === 0);    }    module.exports = isLeapYear;
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