Source of Checksum Calculator

/*This is the "not-yet-browserified" source code of the mnemonic checksum tool found on my website: suttersebastian.com*/

const bitcoin = require('bip39');

window.onload = function () {

    let output = document.getElementById("output");

    document.getElementById("button").addEventListener("click", function () {

        output.innerHTML = "";

        let shortened = false, actual;
        let valid = [];
        let input = document.getElementById("input").value.trim().toLowerCase();

        if (input.length == 0) {
            output.innerHTML = "<p id='red'>NO INPUT GIVEN</p><p id='note'>Please enter a incomplete mnemonic phrase in the gray input field.</p>";
            return;
        }

        for (const word of bitcoin.wordlists.english) {
            if (bitcoin.validateMnemonic((input + " " + word), bitcoin.wordlists.english)) {
                valid.push(word);
            }
        }

        if (valid.length > 0) {

            output.innerHTML = "<p id='green'>Any of these words will work:</p>";

            for (const word of valid) {
                output.innerHTML += word + ", ";
            }

            output.innerHTML = output.innerHTML.slice(0, -2);
        }
        else {
            output.innerHTML = "<p id='red'>INVALID INPUT</p><p id='note'>Check for spelling mistakes and/or incorrect amount of words.<br>Trailing white space and case sensitivity are taken care of.</p>";
        }
    });
}