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kawanet/check-date-bug.js

Created December 1, 2017 05:00
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Safari has a bug on parsing Date when both its time and timezone are negative value.
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check-date-bug.js
/**
* Safari has a bug on parsing Date when both its time and timezone are negative value.
*
* @author @kawanet
* @license MIT
* @see https://github.com/kawanet/timestamp-nano/blob/master/test/52.timezone.js
* @see https://gist.github.com/kawanet/4947237d84ba6efb16183ffcc23e982a
*/
function checkDateBug() {
var date = +new Date("1969-12-31T23:59:59.999-01:00");
return date % 1000 !== 999;
}
if ("undefined" !== typeof module) module.exports = checkDateBug;
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kawanet commented Dec 1, 2017

Safari looks to have a JavaScript bug to give 1 millisecond difference on parsing Date string before 1970 on the Western Hemisphere.

This gist above could detect the environment which has the bug as below:

new Date("1969-12-31T23:59:59.999+01:00").toJSON();
// OK! => "1969-12-31T22:59:59.999Z"

new Date("1969-12-31T23:59:59.999-01:00").toJSON();
// NG! => "1970-01-01T00:59:59.998Z"

The number of (milli)seconds must be 59.999 but NOT 59.998. It gives one millisecond inaccuracy.

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