Time zone offset is added in the wrong direction when parsing dates

[jonathanperret]

Currently, to compute the UTC date, yaml.js adds the time zone offset found in a date literal to the date. Therefore, 2017-01-01T10:00:00+05:00 is parsed as 2017-01-01T15:00:00.000Z:

$ node -p "require('yamljs').parse('date: 2017-01-01T10:00:00+05:00')"
{ date: 2017-01-01T15:00:00.000Z }

This is wrong because +05:00 means the date is written in the local time of the UTC+5 time zone, meaning one should subtract five hours from the local time to get the UTC time (see e.g. https://www.w3.org/TR/NOTE-datetime).

For reference, here's the Date constructor handling the offset correctly:

$ node -p "new Date('2017-01-01T10:00:00+05:00')"
2017-01-01T05:00:00.000Z

[jonathanperret]

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