JSFiddle - React, Tailwind, and code Playground

JavaScript

var ALPHABET = 'ABCDEFGHIJKLMNOPQRSTUWXYZ';
var input = 'ABOZ'
var count = 0;   
    for(x in input) {
        console.log(ALPHABET.indexOf(input[x]),input[x])
        if(ALPHABET.indexOf(input[x])>-1){
            count++;
            continue;
        }
        else{
            break;
        }

    }
if(count==input.length) {
    alert("true");        
}