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<title>Document</title>
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<body>
<script>
String.prototype.weekIndexInYear = function () {
var nowDate = new Date(this != '' ? this : new Date());
var initTime = new Date(this != '' ? this : new Date());
initTime.setMonth(0);
initTime.setDate(1);
initTime.setHours(0);
initTime.setMinutes(0);
initTime.setSeconds(0);
nowDate.setHours(23);
nowDate.setMinutes(59);
nowDate.setSeconds(59);
var differenceVal = nowDate - initTime;
var todayYear = Math.ceil(differenceVal / (24 * 60 * 60 * 1000));
console.log('今年的第几天?',todayYear);
var firstDay = initTime.getDay();
var startDiff;
if (firstDay === 0) {
startDiff = 1;
} else if (firstDay === 1) {
startDiff = 0;
} else {
startDiff = 7 - firstDay + 1;
}
return parseInt(Math.ceil((todayYear - startDiff) / 7));
};
let index = new Date('1/3/2022').toLocaleDateString().weekIndexInYear()
console.log('今年第几周',index);
</script>
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