By default, String.prototype.normalize() uses NFC as an argument. NFC replaces multiple characters with single one.
You can specify "NFC" to get the composed canonical form, in which multiple code points are replaced with single code points where possible.
And here's an example from MDN. It works.
let str = '\u006E\u0303';
str = str.normalize();
console.log(`${str}: ${str.length}`);
But then I decided to try this method with other characters. For example:
let str = '\u0057\u0303';
str = str.normalize();
console.log(`${str}: ${str.length}`);
What's wrong in the second example? Why doesn't it work?