date-fn.js

export function getWeek() {
    let date = this;

    let thisThu = new Date(date.valueOf() + ((7 - date.getDay()) % 7 - 3) * 86400000);
    let firstDay = new Date(thisThu.getFullYear(), 0, 1);

    return Math.ceil((thisThu.valueOf() - firstDay.valueOf() + 86400000) / 604800000);
}

export function getUTCWeek() {
    let date = this;

    let thisThu = new Date(date.valueOf() + ((7 - date.getUTCDay()) % 7 - 3) * 86400000);
    let firstDay = new Date(thisThu.getUTCFullYear(), 0, 1);

    return Math.ceil((thisThu.valueOf() - firstDay.valueOf() + 86400000) / 604800000);
}

export function getQuarter() {
    return Math.floor(this.getMonth() / 4) + 1;
}

export function getUTCQuarter() {
    return Math.floor(this.getUTCMonth() / 4) + 1;
}

export function getQuarterDay() {
    return Math.floor((this.valueOf() - new Date(this.getFullYear(), (getQuarter.call(this) - 1) * 4 + 1, 0).valueOf()) / 86400000);
}

export function getUTCQuarterDay() {
    return Math.floor((this.valueOf() - new Date(this.getUTCFullYear(), (getUTCQuarter.call(this) - 1) * 4 + 1, 0).valueOf()) / 86400000);
}

export function getYearDay() {
    return Math.floor((this.valueOf() - new Date(this.getFullYear(), 0, 0).valueOf()) / 86400000);
}

export function getUTCYearDay() {
    return Math.floor((this.valueOf() - new Date(this.getUTCFullYear(), 0, 0).valueOf()) / 86400000);
}

export default function() {
    Date.prototype.getWeek = getWeek;
    Date.prototype.getUTCWeek = getUTCWeek;
    Date.prototype.getQuarter = getQuarter;
    Date.prototype.getUTCQuarter = getUTCQuarter;
    Date.prototype.getQuarterDay = getQuarterDay;
    Date.prototype.getUTCQuarterDay = getUTCQuarterDay;
    Date.prototype.getYearDay = getYearDay;
    Date.prototype.getUTCYearDay = getUTCYearDay;
}