The left -hand and right hand side of an arithmetic operation must be of type 'any', 'number' or an enum type

I have found out the issue.

The code you have written works only in Javascript

Math.abs(new Date() - new Date(lastConnect)) .

In order to make it work in Typescript, update the code as shown below:

Math.abs(new Date().getTime() - new Date(lastConnect).getTime());

Needless to say, Your code works correctly in Javascript, If you want to get the same result in Typescript, You have 3 options

(1) - With the help of valueOf

let diff = Math.abs(new Date().valueOf() - new Date(lastConnect).valueOf());

(2) - With the help of getTime

let diff = Math.abs(new Date().getTime() - new Date(lastConnect).getTime());
// or
let diff = new Date().getTime() - new Date(lastConnect).getTime();

(3) - With the help of any

let diff = Math.abs(<any>new Date() - <any>new Date(lastConnect))