JSFiddle - React, Tailwind, and code Playground

JavaScript

var string = 'acbACB',
    arr = string.split('');

arr.sort(function(x,y) {
    if(x.toLowerCase() !== y.toLowerCase()) {
        x = x.toLowerCase();
        y = y.toLowerCase();
    }
    return x > y ? 1 : (x < y ? -1 : 0);
});

alert(arr.join(''));