How to make a field required to have a value, with HTML code?

I have html code that was shared with me from Caspio.  The code provides the ability for an individual to sign with their finger or mouse, in a signature box.  One of my issues is that I need this to be filled in and it shouldn't be left blank.  Does anyone know of some lines of code that can be added to require that the field be filled in?  Attached is a copy of the code for your review.... Thanks!

<!-- HTML Block code -->
<div align left>
<div class="sigPad">
    <div class="sig sigWrapper">
        <canvas class="pad" width="600" height="100" style="margin: 0px 0px 0px 0px;  border-style: solid; border-width: 1px; border-color: #bbbbbb #dbdfe6 #e3e9ef #e2e3ea; -webkit-border-radius: 1px; -moz-border-radius: 1px; -o-border-radius: 1px; border-radius: 1px; -webkit-box-sizing: border-box; -moz-box-sizing: border-box; box-sizing: border-box; background-color: #FFFFFF;"></canvas></br>
        <span style="margin: 0px 0px 0px 264px;">
            <input type="reset" class="clearButton" value="Clear">
        </span>
        <input type="hidden" name="output" class="output">
    </div>
</div>
<span class="marker"><strong>Applicant&#39;s Signature</strong></span>
</div>
</div>

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Anthony6890Asked:
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Peter HartCommented:
try:

  <input type="hidden" name="output" class="output"  required>
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Anthony6890Author Commented:
Thank you!
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