nodejs and javascript: get midnight today and convert date formats

While using graphql, I encountered date-format issues. This graphql implementation converts dates to ISOSTRING, such as 2019-11-17T16:00:00.000Z. Here is how to retrieve today's midnight and convert formats.

Get today's midnight

new Date(new Date().toLocaleDateString())
格式为string，显示为：Mon Nov 18 2019 00:00:00 GMT+0800 (中國標準時間)

Get a timestamp

new Date(new Date().toLocaleDateString()).getTime()
格式为number，显示为：1574006400000

Get the current timestamp

Date.now()
new Date().getTime()
格式为number，显示为1574063341624

Parse a date string

var string = "2019-11-20T10:35:26.504Z";
var nowstring = "Mon Nov 18 2019 15:50:35 GMT+0800";
Date.parse(nowstring);
Date.parse(string);
格式为number，显示为1574246126504/1574063435000

Convert to ISO

var isostring = new Date(new Date().toLocaleDateString()).toISOString()
格式为string，显示为2019-11-17T16:00:00.000Z，注意这个ISO标准格式显示是没有时区信息的，也就是中国本地的话是少了8个小时。