JSFiddle - React, Tailwind, and code Playground

HTML

Using split up regex: <input type="text" id="password1" placeholder="Enter password" />
<span id="output1"></span>
<br>
Using one big regex: <input type="text" id="password2" placeholder="Enter password" />
<span id="output2"></span>

JavaScript

function isValid1(pass) {
    return pass.length >= 8 &&    // at least 8 characters
           /\d/.test(pass)  &&    // contains a digit
           /[A-Za-z]/.test(pass); // contains a letter
}

function isValid2(pass) {
    return /^(?=.*[A-Za-z])(?=.*\d).{8,}$/.test(pass);
}

var field1 = document.getElementById("password"),
    output1 = document.getElementById("output"),
    field2 = document.getElementById("password"),
    output2 = document.getElementById("output");

field1.onkeyup = function() {
    output1.innerHTML = isValid(field1.value) ? "Valid" : "Not Valid";
}

field2.onkeyup = function() {
    output2.innerHTML = isValid(field2.value) ? "Valid" : "Not Valid";
}