Day of the Year LeetCode solution in JavaScript

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var dayOfYear = function (date) {
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  let dat2 = new Date(date);
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  let dat1 = new Date(dat2.getFullYear(), 00, 00);
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  let totalTime = dat2 - dat1;
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  return Math.floor(totalTime / 1000 / 60 / 60 / 24);
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};