JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
    <table>
        <tr>
            <th class="current">Today</th>
        </tr>
        <tr>
            <td class="current"><div id="today"></div></td>
        </tr>
    </table>
    <br>
    <form name="estimatedTime">
    <table>
    <tr>
        <td>Weeks:</td>
        <td><input type="text" maxlength=2 id="expTimeinWeeks" name="expTimeinWeeks" value=14></td>
    </tr>
    <tr>
        <td>Date:</td>
        <td><input type="date" name="date" id="date"></td>
    </tr>
    <table>
        <input id="update" type="button" onclick="estimateDate(weeks=expTimeinWeeks.value, date=date.value);  console.log('Form: ' + date.value);" value="Update"><br>
    </form>
    <br>
    <table>
        <tr>
            <th class="estimate">Estimate</th>
        </tr>
        <tr>
            <td class="estimate"><div id="expTime"></div></td>
        </tr>
    </table>
</div>

JavaScript

// Create function to change date.
    function estimateDate(weeks=14, date=now) {
	console.log("Input:  " + date);
        // create new variable 'estimate' with current date
        var estimate = new Date(date);
        console.log("Estimate:  " + estimate);
        // Convert to days
        var inDays = weeks * 7
        // Modify variable 'now' to be (current date time)+(expWeeks variable * 7)
        estimate.setDate(estimate.getDate()+inDays);
        console.log("Modified:  " + estimate);
    
        // Modify DOM 'expTime' with the updated date and return it.
        return document.getElementById("expTime").innerHTML = estimate.toDateString(); 
    };
    // Set variable 'now' to the current date and time.
    var now = new Date();
    // Set variable 'expWeeks' to the time (in weeks) for an estimate from the text input "expTimeinWeeks"
    var expWeeks = document.getElementById('expTimeinWeeks').value;
    // Modify DOM 'today' with the current date and time.
    document.getElementById("today").innerHTML = now.toDateString();
    estimateDate(expWeeks, now);