Javascript "onmousedown" isn't firing

I'm trying to run a function on an element "onmousedown". Here's the code:

<label class="switch">
                  <input type="checkbox" onmousedown="console.log('Run the function'); manageBook(this);"  id="element-id-52"  data-mode= "offx"   >
                  <span class="slider round"></span>
                </label>

But when I click the slider, I don't see either the console.log() message or the function running. Any idea what could be causing this?