Javascript string interpolation gives different result than string concatenation

I ran across a case where Javascript string interpolation is not giving the same result as string concatenation.

Here is a simplified version of the code showing the difference:

const mmt = moment();
console.log('concatenated: ' + mmt); // "concatenated: 1651070909974"
console.log(`interpolated: ${mmt}`); // "interpolated: Wed Apr 27 2022 10:48:29 GMT-0400"
console.log('mmt.valueOf(): ' + mmt.valueOf()); // "mmt.valueOf(): 1651070909974"
console.log('mmt.toString(): ' + mmt.toString()); // "mmt.toString(): Wed Apr 27 2022 10:48:29 GMT-0400"

So my immediate thought was that it was due to a difference in .toString() and .valueOf(), so I made a small test object to verify:

const obj = {
  toString: () => 'toString',
  valueOf: () => 'valueOf',
};

console.log('concatenated: ' + obj); // "concatenated: valueOf"
console.log(`interpolated: ${obj}`); // "interpolated: toString"
console.log('obj.valueOf(): ' + obj.valueOf()); // "obj.valueOf(): valueOf"
console.log('obj.toString(): ' + obj.toString()); // "obj.toString(): toString"

However, when I tried this with a Date object (which also has a different result from .toString() vs .valueOf()), I do not get the same behavior--this time interpolation and concatenation both use the .toString() value:

const dte = new Date();
console.log('concatenated: ' + dte); // "concatenated: Wed Apr 27 2022 10:48:29 GMT-0400 (Eastern Daylight Time)"
console.log(`interpolated: ${dte}`); // "interpolated: Wed Apr 27 2022 10:48:29 GMT-0400 (Eastern Daylight Time)"
console.log('dte.valueOf(): ' + dte.valueOf()); // "dte.valueOf(): 1651070909974"
console.log('dte.toString(): ' + dte.toString()); // "dte.toString(): Wed Apr 27 2022 10:48:29 GMT-0400 (Eastern Daylight Time)"

So my questions is: What are the actual rules for how an interpolated value is converted to a string when concatenated vs interpolated, and why does Date seem to be different from other objects? (I have tried to look this up, but thus far my googling has been unsuccessful...)

JSFiddle Example