JSFiddle - React, Tailwind, and code Playground

JavaScript

var a = "hello";
var b = "hell";

a = "modern";
b = "modem";

a = "jQuery";
b = "Javascript";

a = "jQuery";
b = "javascript";

function similitude(a, b) {
    for (var i = 0, len = Math.max(a.length, b.length); i < len; i++)
        if (a.charAt(i) != b.charAt(i)) 
            return Math.round(i / len * 100);
}

document.write("Similitude: " + similitude(a, b) + "%");