javascript - Google Maps Time Zone API get local time in UTC

Question

Google Docs says:

The local time of a given location is the sum of the timestamp parameter, and the dstOffset and rawOffset fields from the result.

timestamp + dstOffset + rawOffset = local time in seconds in UTC

Problem

I am trying to get the local time in the correct time zone. I thought that new Date(timestamp + dstOffset + rawOffset *1000) would return the local time in UTC, but instead I find that the actual numerical values are indeed in local time, in the wrong time zone (UTC).

Example:

timestamp: 1456349190

readable timestamp: new Date(1456349190*1000).toGMTString() (Wed, 24 Feb 2016 21:26:30 GMT)

https://maps.googleapis.com/maps/api/timezone/json?location=39.2079206,-84.5274616&timestamp=1456349190&key=${googleApiKey}

Returns:

• dstOffset: 0
• rawOffset: -18000
• timeZoneId: America/New_York

Data:

Sum in seconds = 1456349190 + 0 + (-18000) = 1456331190

Sum in milliseconds = 1456331190*1000 = 1456331190000

Supposed Local Date = new Date(1456331190000).toGMTString() (Wed, 24 Feb 2016 16:26:30 GMT)

Question

Shouldn't readable timestamp and Supposed Local Date be the same since both are in UTC? Seems like Supposed Local Date should really be Wed, 24 Feb 2016 16:26:30 EST

Is this correct?

If so it seems like I just need to extract the values I need (local hour) from Supposed Local Date and apply the correct time zone returned from google api timeZoneId (America/New_York) because 16:26:30 is the correct local time I need.

Helpful Tips

These are some guidelines that helped me understand timestamp better:

"The unix timestamp isn't affected by a timezone setting. Setting the timezone only affects the interpretation of the timestamp value."

Answer 1

Timestamp value indicates the seconds since 1/1/1970 UTC. Not local timestamp.

The Google API tells you the rawOffset of location is "-18000"

When you calculate the date with timestamp, you should align the unit in UTC. Because Date class treats the timestamp as UTC.

In your explanation, the value 1456331190000 is a local timestamp, but the Date class treats the value as UTC.

This is your mistake point.

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Here is the code (in Node.js)