charCodeAt and fromCharCode do not return the same character

Question

In theory, no matter what the input is, the output should be unchanged:

String.fromCharCode("a".charCodeAt(0));    //"a"

This makes sense because I'm just trying to get the char code of a character, and then casting it back to a character.

However when I try with this character, it breaks:

//"🌀": 55356
String.fromCharCode("🌀".charCodeAt(0));    //"�" (65533)

^{(Note that I actually highlighted the string and pasted it into the next line. It changed to � by itself for some reason.)}

Why is this happening and how can I fix this?

I noticed that there is a new method in ES6, String.fromCodePoint() but it is not supported every browser except Firefox.

Answer 1

It does not change.

> String.fromCharCode("🌀".charCodeAt(0)).charCodeAt(0)
  55356

And you can check all by:

for (var i = 0; i <= 65535; i++) {
   if (String.fromCharCode(i).charCodeAt(0) !== i) {
       console.log('error', i, String.fromCharCode(i)); 
   }
}

Why you saw � is because �(65533) is used to replace a character whose value is unknown or unrepresentable in unicode.

It is called REPLACEMENT CHARACTER.