convert chatham time to gmt in javascript

To convert Chatham time to GMT in Javascript, we can use the getTimezoneOffset() method of the Date object. Chatham time is in GMT+12:45 time zone, meaning it is 12 hours 45 minutes ahead of GMT. So, to get the corresponding GMT time, we can subtract 12 hours 45 minutes from the Chatham time. Here's an example code snippet:

index.tsx
// create a new Date object representing the Chatham time
const chathamTime = new Date();

// get the timezone offset in minutes and convert it to milliseconds
const tzOffsetInMs = chathamTime.getTimezoneOffset() * 60 * 1000;

// subtract 12 hours 45 minutes from the Chatham time to get the GMT time
const gmtTime = new Date(chathamTime.getTime() - (12 * 60 + 45) * 60 * 1000 - tzOffsetInMs);

// format the GMT time as a string
const gmtTimeString = gmtTime.toUTCString();

console.log(`Chatham time is ${chathamTime.toLocaleString()}, corresponding GMT time is ${gmtTimeString}`);
584 chars
14 lines

Note that the getTimezoneOffset() method returns the difference, in minutes, between the local time zone and UTC/GMT. So, we need to multiply it by 60*1000 to convert it to milliseconds. Also, we subtract the timezone offset from the Chatham time so that we can get the correct GMT time. The resulting gmtTime object represents the corresponding GMT time, which we can format as a string using the toUTCString() method.