Regex to Upper Case all words but exclude ' (apostrophe)

Question

I'm trying to build a funct to UpperCase all the string words but I'm having a problem with the following:

String.prototype.upper = function() {
    return this.replace(/[^a-zA-Z0-9]+(.)/g, chr => chr.toUpperCase())
 }


let str = "My uncle's car is red";
console.log(str.upper()) 


//My Uncle'S Car Is Red

I need to exclude the S from being UpperCased, after the apostrophe.

Any ideas how this can be done?

Thank you