How to use 'add timezone offset to date javascript' in JavaScript

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function timeZoneGetter(date) {
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    var zone = -1 * date.getTimezoneOffset();
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    var paddedZone = (zone >= 0) ? "+" : "";
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    paddedZone += padNumber(Math[zone > 0 ? 'floor' : 'ceil'](zone / 60), 2) +
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        padNumber(Math.abs(zone % 60), 2);
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    return paddedZone;
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}

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function timezoneAbbr(date){
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    // Date.toString gives different results depending on the
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    // browser/system so we fallback to timezone offset
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    // chrome: 'Mon Apr 08 2013 09:02:04 GMT-0300 (BRT)'
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    // IE: 'Mon Apr 8 09:02:04 UTC-0300 2013'
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    var tz = /\(([A-Z]{3,4})\)/.exec(date.toString());
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    return tz? tz[1] : timezoneOffset(date);
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}