Unary Plus: Converting Date Objects to Millisecond Timestamps

In JavaScript, you might encounter code that resembles:

function fn() {
  return  new Date;
}

This expression returns a timestamp representing the current time, rather than a full Date object. However, it's not immediately apparent what the plus sign ( ) does.

The answer lies in the unary plus operator. When applied to a value, it performs a to-number conversion. In this case:

let numMilliseconds =  new Date;

is equivalent to:

let numMilliseconds = Number(new Date);

The Number function converts the Date object into a number, representing the number of milliseconds since the start of the Unix epoch (midnight UTC on January 1, 1970).

This technique is commonly used when you only need a timestamp, saving memory and eliminating the need to manually extract it from the Date object. Consult the MDN documentation and "XKCD: Unary Plus" for further insights.