You can get JS to work, but you must make sure it is evaluated at runtime like this (otherwise it is static):

const timestamp = () => {};
timestamp.toString = function() {
    const date = new Date();
    const hours = date.getHours().toString().padStart(2, '0');
    const minutes = date.getMinutes().toString().padStart(2, '0');
    const seconds = date.getSeconds().toString().padStart(2, '0');
    const milliseconds = date.getMilliseconds().toString().padStart(3, '0');
    return `${hours}:${minutes}:${seconds}:${milliseconds}`;
};

// log with a mark, color, and timestamp
// e.g.: 
// 08:35:01:232 [LOG]  This log message shows a red tag and timestamp
log = console.log.bind(console, `%s %c[LOG] `, timestamp, `color:#FC0`);

// then:
log('Hello World');

I use it everywhere in my code to better identify classes/modules, etc… in the console.
You can also use it in node to show timestamps in files.

Go to Facebook and open up the browser console. They use it for something useful.

Use case: fun.

It is not because you CAN that you SHOULD…

I cannot think of a use case where this feature would be useful.

Prove me wrong.