Date.now() returns a unix timestamp in milliseconds.
const now = Date.now(); // Unix timestamp in milliseconds_x000D_
console.log( now );Prior to ECMAScript5 (I.E. Internet Explorer 8 and older) you needed to construct a Date object, from which there are several ways to get a unix timestamp in milliseconds:
console.log( +new Date );_x000D_
console.log( (new Date).getTime() );_x000D_
console.log( (new Date).valueOf() );