Javascript to MySQL Datetime format

I have a Javascript file that populates 2 grids with data from 2 different tables in MySql. In the one grid, the format of the date looks like this: "1970-01-01T04:15:00.000+0000". In the other, it looks like this: "1663286400000". The fields in the two tables are the same; both are DATETIME. Any idea why this is happening?