Date.prototype.toISOString()
  The toISOString() method returns a string in
  simplified extended ISO format (ISO 8601), which is always 24 or 27
  characters long
  (YYYY-MM-DDTHH:mm:ss.sssZ
  or
  ±YYYYYY-MM-DDTHH:mm:ss.sssZ,
  respectively). The timezone is always zero UTC offset, as denoted by the suffix
  "Z".
Syntax
toISOString()
Return value
A string representing the given date in the ISO 8601 format according to universal time.
Examples
Using toISOString()
let today = new Date('05 October 2011 14:48 UTC')
console.log(today.toISOString())  // Returns 2011-10-05T14:48:00.000Z
The above example uses parsing of a non–standard string value that may not be correctly parsed in non–Mozilla browsers.
Specifications
| Specification | 
|---|
| ECMAScript Language Specification  # sec-date.prototype.toisostring  | 
Browser compatibility
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